Fungi, including those pathogenic to humans and animals, are eukaryotic microorganisms that can be conveniently separated into two basic groups, moulds and yeasts. Moulds consist of those fungi that grow in a filamentous form, whereas yeasts are characterized by solitary cells that reproduce by budding. Their nucleus like that of other eukaryotic organisms contains a nucleolus and several chromosomes that are bound by a nuclear membrane. Hyphal cells in septate hyphae may be uninucleate, binucleate or multinucleate. For the most part cellular and nuclear division are independent events especially with respect to vegetative growth. As in other eukaryotic organisms, fungi have mitochondria, 80s ribosomes and centrioles. The cell wall of fungi consists of chitin, chitosan, glucan, mannan and other components in various combinations. Fungi are carbon heterotrophs therefore they require preformed organic compounds as carbon sources.
The actinomycetes are prokaryotic gram positive filamentous bacteria. The actinomycetes serve as a host to bacteriophages, whereas fungi cannot serve as their host. These organisms are sensitive to antibacterial agents such as penicillin but not to antimycotic agents such as amphotericin B. The opposite is true for fungi. Historically, because of their microscopic morphology, some actinomycetes have been studied by medical mycologists.
Most fungi are found in the soil and on other organisms, a few are aquatic. However, many can be spread by water through soil erosion and as spores in aerosols. Most require moist conditions and warmth and the tropic are more conducive to fungal diseases than temperate regions. Many are opportunistic pathogens and some cause fatal central nervous system infections. They are not often recognized as waterborne pathogens as are the viruses and bacteria. Fungi are more often diseases of water used for recreation, bathing, hot tubs, swimming, washing and water uses other than drinking, in contrast to many viral and bacterial diseases which occur from ingestion of the water.
Fungi are very different from bacteria. In many ways fungal cells are more like animal cells. They have multiple chromosomes in a nucleus within a nuclear membrane. They have cytoplasmic organelles. They do have a cell wall but its composition is quite distinct from the cell wall of bacteria. A mould differs from yeast. Moulds grow as a complex mass of multi-cellular interlocking strands made of cells joined end to end, a mycelium, they have a complex reproductive process involving specialised structures that release air borne spores. Yeasts are unicellular fungi that reproduce by binary fission though sometimes the cells become quite long and bear a superficial resemblance to mycelia. Some fungi have yeast like and mould like forms. These are known as dimorphic fungi. Many of the pathogenic fungi are dimorphic fungi with a mould like environmental form and the yeast like form associated with infection.
Constant exposure to fungal spores in the atmosphere can induce respiratory allergies. Elevated antibodies to a range of common spore forming fungi have been demonstrated in occupational diseases such as Humidifier fever, Malt workers' lung, Farmers' Lung and Wheat threshers' disease. Certain fungi, such as mushrooms, can produce poisonous toxins that may prove fatal if ingested, Amanita phalloides, others, Psilocybe, affect the central nervous system inducing hallucinogenic responses. Many moulds produce secondary metabolites that are highly toxic to humans. Ergotism is caused by eating bread prepared from rye infected with the fungus Claviceps purpurea. Historically, several large scale outbreaks of madness in local populations have been attributed to ergotism.
Owing to the dramatically increased incidence of life-threatening opportunistic fungal infections, due to HIV/AIDS, chemotherapy, organ transplants, antibiotic treatment and other conditions where the immune system or natural flora is deliberately or concomitantly suppressed, it is now clear that diseases of fungal infection are of major importance. The rise in cases has been particularly apparent in transplant recipients and especially in AIDS patients. Besides more serious infections associated with these vulnerable groups, superficial infections such as ringworm and thrush have also become more prevalent. Despite recognizing the importance of fungi as a cause of disease in Man and animals, many of the more serious fungal infections remain difficult to diagnose and treat.
IntroductionIn 1835, Agostino Bassi published his classic research paper entitled Del mal del segno, Icalcinaccio o moscardino, in which he reported upon his experimental work demonstrating for the first time that a microorganism, the fungus Beauvaria bassiana, could cause disease in an animal, the silkworm. Two years later, Robert Remak observed the presence of hyphae in the crusts associated with tinea favus. His observation was important because he was the first to incriminate a microorganism as the cause of human infection. Following these two important contributions, David Grub reported in 1841 that he had isolated a fungus from a case of ringworm and then experimentally showed that the fungus could cause ringworm when inoculated onto normal skin.
Human fungal infections are uncommon in normally healthy persons in the temperate zones, usually being confined to conditions such as candidiasis (thrush) and dermatophyte skin infections such as athlete's foot. However, in the immunocompromised host, a variety of normally mild or nonpathogenic fungi can cause potentially fatal infections. Furthermore, the relative ease with which people can now visit exotic countries provides the means for unusual fungal infections to be imported to temperate areas.
Most of the fungal species recognised as capable of causing disease (mycosis) in man and animals are moulds but there are a number of pathogenic yeasts. Dimorphic fungi usually assume a mould form when growing as saprophytes in nature and adopt a yeast form that can cause infection in animals. There is considerable variation in the pathogenicity of these fungi: some are highly pathogenic and capable of establishing an infection in all exposed individuals, for example the systemic pathogens Histoplasma capsulatum and Coccidioides immitis; others, such as Candida and Aspergillus species, are opportunist pathogens, which ordinarily cause disease only in an immunocompromised host.
Diseases caused by fungi are known as mycoses (mycosis). Over 50 different fungi from among the bread molds, cup fungi and the imperfect fungi have been reported to infect humans. The number of people infected by fungi has increased recently. There are more people in the population with weak immune systems, due to chemotherapy, organ transplants and HIV/AIDS, as examples. Ironically, cyclosporin, a fungal-derived drug that reduces the risk of rejection in organ transplants, weakens the immune system so that other fungi may infect the patient. Increased exposure may contribute to the increase in fungal infections. Adding insulation to a house, for example, restricts air exchange with the outside and one effect of this may be increased humidity which encourages mold growth.
Poisoning caused by fungi can be separated into two principal groups: mycetism and mycotoxicoses. Mycetismus, or mushroom poisoning, results from the ingestion of a mushroom that contains preformed toxic metabolites. Based upon the major ingredients present, mycetismus can be separated into at least eight major groups. These range from cellular destruction, liver damage and kidney damage, to death, usually occurring in approximately 10 hours when a mushroom like Amanita phalloides containing amanitine is ingested. Gastrointestinal irritants produced by a number of mushrooms result in nausea, vomiting, cramps and diarrhea. Other mushrooms like Psilocybe produce compounds such as psilocybins and psilocins that affect the central nervous system resulting in hallucinogenic behavior.
Mycotoxicosis consists of an intoxication following the ingestion of preformed substances produced by fungi when they grow on foodstuffs. These substances, mycotoxins, are produced when the fungus grows in specific environments, on particular substrates, under certain conditions and by only specific strains of the species. Of the mycotoxicoses, the most famous is ergot, which is noted for hallucination and vascular necrosis. Claviceps purpurea, the fungus that causes ergotism, has had a profound impact upon the history of various peoples for hundreds of years. In veterinary medicine, mycotoxins such as the aflatoxins, or those that cause toxic alimentary aleukia and stachbotryotoxicosis, are among the best known. These mycotoxins have resulted in the death of extremely large numbers of animals over the years.
Some allergists now think that a very high percentage of the chronic year-round allergies in the population may be caused by fungal spores. The number of people affected is increasing, probably due to increased awareness and changes in building construction. New homes are tighter so air is not mixed with outside air as often as in older homes. Many molds grow in damp walls and the number of spores can reach very high levels in air-tight homes. One study estimates that about 1% of homes in the USA contain toxic molds. The molds involved include Aspergillus and Penicillium. The gorilla fungus, Stachybotrys atra, has recently received a lot of attention in the press because it been linked to infant deaths and headaches, nose bleeds and sinus problems in adults.
Allergic diseases caused by fungi typically consist of hypersensitivity to the inhalation of fungal spores, conidia or fungal fragments. Hypersensitivity pneumonitis with cough, fever, lethargy and pulmonary infiltrates may result following the patient's exposure to conidia produced by fungi like Alternaria alternata or basidiospores of the Lycoperdon mushroom. Fungi such as Aspergillus fumigatus can cause allergic aspergillosis that may be seen as extrinsic asthma, extrinsic allergic alveolitis or allergic bronchiopulmonary aspergillosis. Hypersensitivity may occur in association with the state of colonization seen with a fungus ball that forms in the bronchus. A similar process occurs in the nasal sinuses, where fungus balls can be developed by many fungi such as Bipolaris spicifera in patients who have apparently normal immune systems. In this situation the fungus grows in the nasal cavity where it serves as a continuous source of antigen to which the adjacent tissue responds.
Fungal Infection ClassificationAs with many areas of science, there has been disagreement regarding the clinical nomenclature for the fungal mycoses. Many of these problems can be traced to a misunderstanding of, or disagreement about, the conceptual basis for naming fungal infections. As a result the names of fungal diseases are often quite confusing and difficult for the non-specialist to understand. Ideally, the terminology to describe the mycoses should be applied in a consistent and unambiguous manner. The nomenclature selected should have enough depth and clarity to accommodate advances in diagnosis, patient management, the basic biology of the pathogens, taxonomic reclassifications, new pathogens and a clearer understanding of host-pathogen interactions. To achieve such a nomenclature it is important to understand the fundamental difference between the concepts of disease and infection. Infection does not necessarily lead to disease. In addition, contamination does not necessarily imply infection.
Disease occurs when there is functional and structural harm in the host that is accompanied by signs and symptoms such as pain, heat, swelling, redness, fever, weight loss, fatigue, lassitude, radiographic manifestations, draining sinuses and purulent exudates. In contrast, infection is the invasion and replication of an organism in the host's viable tissue. In an infection disease may or may not be present. During sub-clinical infectious diseases infection is present without clinical manifestations, even though there is some damage to the host. A fungus capable of causing an infectious disease is known as a pathogen. To be a successful pathogen the fungus must find a suitable host niche where it can replicate. Virulence is a measure of pathogenicity, which is an assessment of the likelihood that disease will occur. Some fungi may serve as pathogens at one time and then be recovered later as contaminants. A primary pathogen is a fungus that typically causes disease in some portion of susceptible individuals who apparently have intact specific and nonspecific defense systems. Host defense mechanisms are important because they prevent or delay the pathogen from gaining access to the host and causing invasive disease.
In terms of infection we can think of fungi in two main groups. There are pathogenic fungi which can cause infection in people who appear otherwise healthy. The most common of these are the dermatophyte fungi that cause ring-worm, an infection of the superficial layers of epidermis. Ringworm is often self-limiting and generally easily treated. Dermatophyte infection may be associated with contact with animals but spread from person to person also occurs. Athlete's foot is an even more common superficial infection of the epidermis of the skin. The fungus spreads rapidly in communal changing and showering areas. Other pathogenic fungi include Histoplasma capsulatum.
In general most of the invasive pathogenic fungi are associated with specific areas of the world. They exist primarily in soil as moulds but can generate spores. The spores may be dispersed in the air and can be inhaled into the lungs. In specific geographic areas a very high proportion of people have evidence of previous, self-limiting infection with local pathogenic fungi if tested for antibodies to these fungi. A small proportion of otherwise healthy people infected with these pathogenic fungi develop progressive disease. The disease may only develop many years after primary infection. In many cases the pathogenic fungi are mainly associated with pulmonary disease, with features resembling tuberculosis. Only a minority of infected people develop progressive disease, as is the case with tuberculosis. People who have lived in areas endemic for such fungi may develop, many years later in other parts of the world, an illness related to reactivation of a persistent, latent, fungal infection. A travel history over the lifetime of the person may be very valuable in diagnosing some inexplicable disease.
Most fungi are opportunistic and do not infect or cause disease in normal healthy people with uncompromised immune systems; they are only a problem in immunocompromised patients where they are a major cause of morbidity and mortality in AIDS/HIV patients. For people in the late stages of AIDS, transplant and major surgery patients and others that have had extensive invasive procedures, fungal infection is a major concern and the term non-pathogenic has no meaning. To describe an organism as non-pathogenic means that it is the kind of organism with no potential to overcome the normal defences against infection. People with such conditions have virtually no defences. Their skin is penetrated by intravenous lines, the mucosa of their bowel is often damaged by chemotherapy, their normal bacterial flora is destroyed by antibacterial agents and their immune system is virtually non-functional. Such people can be infected and killed by almost anything including bread mould fungus. The principle fungi causing problems are the yeasts, Candida albicans and the moulds Aspergillus and Mucor.
Opportunistic pathogens typically do not cause disease in people who have intact host defense mechanisms. Rather, they cause disease in compromised hosts. Colonization occurs when fungi replicate either in or on host tissue and are seen by microscopy on host tissue or they are isolated in culture. Contamination consists of the mere presence of fungi on the surfaces of the host. The challenge confronting the development of a clinical nomenclature involves implementing these types of possibilities into the terms that characterize the mycoses. It is important to distinguish two concepts that are concurrently used in naming mycoses.
The first concept deals with instances in which a single case or only a few cases are known. Here the taxonomic classification of the pathogen and the pathology of the infection can be united to form a meaningful expression. For example, a description such as endocarditis caused by Exserohilum rostratum provides details regarding the infectious disease and its etiology. The second concept encompasses conveying a common theme of infection, which could involve several taxonomically different fungi. An expression such as subcutaneous phaeohyphomycosis summarizes the pathology, pathogenesis, management and prognosis for a situation that is caused by a number of different black fungi.
Since there are over 400 species of fungi that have been demonstrated as capable of causing a wide spectrum of infections and diseases, and there is a constant discovery of new pathogens, there is a need for a robust, consistent and clear clinical nomenclature for the mycoses. Mycoses can be classified as superficial, cutaneous, subcutaneous, opportunistic and systemic, depending upon the organs involved and the host-pathogen interactions. Fungal infections or mycoses can be classified depending on the degree of tissue involvement and mode of entry into the host.
The use of fungal names as part of the clinical nomenclature is inappropriate because they limit the concept too much and are subject to change as the taxonomy of the pathogens changes. The numerous clinical terms-allescheriosis, allescheriasis, monosporiosis, petriellidiosis, and pseudallescheriasis-that have been created as a means to parallel the taxonomic changes associated with Pseudallescheria boydii provide an excellent example of this problem.
The dimorphic fungi are characterized by growing as moulds at 25 to 30 degrees Celcius and in a second morphologic form at both 37 degrees Celcius and in the host. The nomenclature used for mycoses caused by the dimorphic fungi is based upon the generic names of the pathogens. Since these fungi for the most part represent monotypic genera that are stable their taxonomy will remain constant. This is also the situation with yeasts like Candida albicans and Cryptococcus neoformans. A major problem arises when the nomenclature for mycoses is based upon the taxonomic classification of the pathogen whose taxonomy may be changed. It is for this reason that the clinical nomenclature used for fungal infections should be based upon well considered terms that reflect the host pathogen interaction rather than one based upon the taxonomic classification of the pathogen. A great deal of thought is required for naming infections caused by fungi.
The number of new opportunistic pathogens is rapidly increasing as is the number of different types of infections that they are capable of causing in immunocompromised hosts. The proliferation of names for new mycoses based upon the generic name of the fungus involved is counterproductive and simply leads to additional confusion. It is hoped the use of descriptive terms reflecting the infection and a concurrent designation of the etiologic agent will be used until enough cases are known where common themes of disease become evident. At this time, conceptually based clinical terms should be formulated.
Fungal infections may be classified according to the type of tissues they infect and the extent of their infection.
Dermatophytes are fungi that have the ability to invade and grow on keratinized, or non-living tissues, on the living host. There are fungi which are keratinophilic, but which don't grown on a living host. For example, Chrysosporium indicum or Chrysosporium keratinophilum will grow on keratin, but only if the keratin is completely separate from the host. Feathers, animal hooves, hair and animal skin all can be used as growth substrates for the keratinophilic fungi. These types materials are used to isolate keratinophilic from soil and other environments where these fungi grow.
The clinical nomenclature for the fungal infections of the hair, nail, skin, and subcutaneous tissues is often confusing. The terms overlap, some of the terms sound like names of fungi, but aren't, and different definitions may be encountered in different texts. Terminology such as cutaneous phaeohyphomycosis and cutaneous hyalohyphomycosis may be applied to colonization of the cutaneous tissues when there is a need for a general term. Phaeohyphomycosis is used for infections due to melanin-producing, or dematiaceous, species of moulds. Melanin is a black pigment, and fungi that produce melanin are visibly black or brown. The term applies to fungal structures in tissue or clinical specimens whether or not the melanin is visible without special stains. Hyalohyphomycosis is a term which parallels phaeohyphomycosis, but is used for infections due to species of moulds which do not produce melanin or are not dematiaceous. Dermatophytosis, a colonization caused by dermatophytes, is commonly referred to as ringworm or tinea.
Cutaneous mycoses are characterized by damage caused by the proliferation of fungi in the feathers, hair, nails and skin. These structures all contain keratin, a tough, fibrous protein. They also attack scales, and even the lens of the eye, because it, too, contains keratin. There is obvious tissue damage, the non-living layers are usually involved, and an immune response can be measured. Such superficial infections are the most common and widespread mycoses. The fungi causing dermatomycoses are common soil fungi. Their biology in the soil enable these fungi to also invade and absorb nutrients from the keratinized areas of the body. The most common genera of fungi causing dermatomycoses are Microsporum, Epidermophyton and Trichophyton.
Dermatologists often call dermatomycosis, tineas, because these diseases resemble infections that are caused by parasitic worms burrowing beneath the skin. Each mycosis was given a Latin binomial based on where the infection occurs: Tinea capitis (on the head), Tinea barbae (on the beard), Tinea corporis (on the body), Tinea cruris (on the groin), Tinea pedis (on the foot). Common names for these infections include tems such as athletes foot, ringworm, and jock itch. Ringworm refers to the characteristic central clearing that often occurs in dermatophyte infections of the skin. All occur in the temperate zones although tinea infections, other than pedis, are now rare.
Fungi such as Piedraia hortae colonize tissues such as hair. The fungus forms a fruiting body called an ascostroma around a hair shaft. The ascostroma is hard, carbonaceous, black and tightly attached to the hair shaft. There is a little tissue damage only at the site where the ascostroma is attached to the hair shaft. The mycosis is known as superficial phaeohyphomycosis, or black piedra. A similar colonization caused by Trichosporon beigelii on hair is known as superficial hyalohyphomycosis, or white piedra.
Candida albicans is a yeast causing candidiasis or "thrush" in humans. As a superficial mycoses, candidiasis typically infects the mouth or vagina. Candida albicans is part of the normal flora of the vagina and gastrointestinal tract and is termed a commensal. However, during times of ill health or impaired immunity the balance can alter and the organism multiplies to cause disease. Antibiotic treatment can also alter the normal bacterial flora allowing Candida albicans to flourish.
Deep mycoses infect tissues below the epidermis. These mycoses are not as infectious as the dermatomycoses mainly due to the difficulty of dispersing spores from within tissue. Deep mycoses are now appearing outside of historic areas of infection because of air travel. Deep mycoses are classified into two subgroups.
Subcutaneous mycoses consist of a heterogeneous group of infections caused by a broad spectrum of taxonomically diverse fungi. The fungi gain entrance to the subcutaneous tissues usually following punture wounds, where they remain in localized micro-environmental niches associated with abscess formation. Tissue damage is variable, and the immune system recognizes the fungi. The spectrum of infection includes phaeohyphomycosis, hyalohyphomycosis, chromoblastomycosis, mycetoma and similar mycoses. Subcutaneous mycoses tend to remain localized and rarely result in systemic infections.
Subcutaneous mycoses are infections confined to the dermis, subcutaneous tissue or adjacent structures. Infection may arise following the wounding of the skin and the introduction of vegetable matter. These mycoses are rare and confined mainly to tropical regions. They tend to be slow in onset and chronic in duration. An example is sporotrichosis caused by Sporothrix schenckii. The fungus is dimorphic, being a mould that can convert to a yeast form during infection. Sporotrichosis was once common in Europe but cases are now rare. The disease is most prevalent the Americas, South Africa and Australia. Infection usually follows an insect bite, thorn prick or scratch from a fish spine. Certain occupation groups appear to have increased risk from infection. These include florists, farm workers and others who handle hay and moss. The most common symptom is a ulcerative lesion that may develop into lymphangitis.
Systemic mycoses, primary and opportunistic, are invasive infections of the internal organs with the organism gaining entry via the lungs, gastrointestinal tract or through intravenous lines. They may be caused by primary pathogenic fungi or by opportunistic fungi that are of marginal pathogenicity but can infect the immunocompromised host.
These mycoses infect internal organs, and, in some cases, the skin and its underlying tissues. They may be asymptomatic. Most infections are self-limiting and mild, but others can be acute or chronic and if a vital organ such as the brain is involved death may result. The fungi causing systemic mycoses are either filamentous, or one of several unicellular yeasts. The hyphae of the filamentous fungi often disintegrate to produce a yeast phase which helps the fungus spread throughout the body. This ability to exist in either the filamentous or yeast forms is termed diphasic or dimorphic. In systemic mycoses the pathogen disseminates from one organ to another. Frequently, systemic mycoses originate in the lungs, where the pathogens disseminate by the hematogenous route. Most of the dimorphic fungi, yeasts and dangerous opportunistic pathogens are capable of causing systemic mycoses. There is typically tissue destruction and an evident host response.
Systemic mycoses generally result from the inhalation of airborne spores of pathogenic moulds that may be present as saprophytes in soil and on plant material. These infections typically start with a primary pulmonary infection that is often asymptomatic. In some cases they progress to cause a secondary disseminated disease that is life-threatening. Systemic mycoses due to opportunistic pathogens such as Aspergillus, Candida and Cryptococcus species have a more widespread geographical distribution. As modern medicine advances, serious opportunistic mycoses are being seen with increasing frequency in patients compromised by disease or drug treatment. In transplant patients, opportunistic systemic mycoses are among the most frequent causes of mortality due to infection.
With primary pathogenic fungi infection occurs in previously healthy persons and arises through the respiratory route. Examples include histoplasmosis, blastomycosis, coccidiomycosis and paracoccidiodomycosis. The fungi occur throughout the world. Histoplasmosis is caused by Histoplasma capsulatum. The organism is dimorphic, a mould that can convert to a yeast form. Histoplasma capsulatum is endemic in many parts of the world including North and South America. It is found in the soil and growth is enhanced by the presence of bird and bat excreta. Environments containing such material are often implicated as sources of human infection. The lungs are the main site of infection but dissemination to the liver, heart and central nervous system can occur. Pulmonary infection can resemble symptoms seen in tuberculosis.
These fungi attack patients that have some serious immune or metabolic defect, or have undergone surgery. The diseases include aspergillosis, systemic candidosis and cryptococcosis. Fungi that are normally not pathogenic, such as Trichosporon, Fusarium or Penicillium, may cause systemic infections in immunocompromised patients. Aspergillosis is the name given to a number of different diseases caused by the mould Aspergillus. It produces large numbers of spores and occurs world-wide. Aspergillis fumigatus is one of the most common species causing disease. The organism can infect the lungs, inner ear, sinuses and, rarely, the eye of previously healthy persons. In the immunosuppressed host, Aspergillus can disseminate throughout the body.
In severely immunocompromised patients, those receiving chemotherapy, Candida albicans, a part of the normal human flora, can proliferate and disseminate throughout the body. Cryptococcosis is a systemic infection caused by the yeast Cryptococcus neoformans. The commonest manifestation is a subacute or chronic form of meningitis resulting from the inhalation of the organism. Pulmonary infection can also occur. The disease affects both healthy and immunosuppressed individuals and occurs world-wide.
The three most dangerous systemic mycoses caused by yeasts include.
Some of the other potentially fatal systemic mycoses are caused by the following species of fungi
Fungal Disease Descriptions
AspergillosisAspergillis is a ubiquitous genus of fungi found in soil, on plants and in water. Some of the most important Aspergillis species, all of which grow as mycelial fungi with septate hyphae and form distinctive sporing structures by which they may be identified, include:
Aspergillosis most frequently affects the lungs and can take a number of clinical forms. Extra-pulmonary infections at sites such as the nasal sinuses and superficial tissues may also occur. Inhalation of Aspergillus spores may lead to colonization of existing lung cavities (aspergilloma form) or a hypersensitivity reaction (allergic aspergillosis). Allergic aspergillosis typically becomes chronic, whereas colonization may remain chronic or become invasive. It must always be remembered that a number of other fungi can be morphologically identical to Aspergillus in tissue.Rarely, Aspergillus may cause invasive disease of the lung from where it may disseminate to other organs. This form of disseminated aspergillosis is seen in patients who are severely immunocompromised.
Allergy to Aspergillus species is usually seen in atopic individuals with elevated IgE levels. About 10-20% of asthmatic patients have an allergic response to Aspergillus fumigatus. Asthma with eosinophilia is a more chronic form if aspergillosis. It can result in progressive lung damage. In Allergic Bronchopulmonary Aspergillosis(ABPA) the mould colonises the mucosal surface of the lower respiratory tract but does not invade. There is an intense hypersensitivity response to the Aspergillu antigens and impairment of lung function. This syndrome is observed as a complication in some asthmatics and is associated with marked impairment of pulmonary function and abnormal findings on chest X-ray. Farmers Lung is a syndrome of shortness breath typically occurring several hours after exposure to mouldy hay. Antibodies (IgG type NOT IgE ) form a precipitate with Aspergillus antigen in the alveolar walls and an inflammatory cascade is initiated.
In this form of aspergillosis, sometimes referred to as fungus ball, the fungus colonizes pre-existing cavities in the lung, particularly old tuberculosis lesions, and forms a compact ball of mycelia. Eventually the resulting aspergilloma becomes surrounded by a dense fibrous wall. Although these lesions are generally discrete, the fungus may invade the surrounding tissue and spread throughout the body in patients who become immunosuppressed. Fungal balls are usually solitary and vary in size. They are, however generally less than 8 cm in diameter. Radiologically they appear as a well-defined mobile opacity within a cavity, usually with a crescent of air at the upper margin. Patients are either asymptomatic or have only a moderate cough and sputum production. Occasional haemoptyses may occur particularly when the fungus is actively growing. Haemorrhage following invasion of a blood vessel is one of the serious complications associated with this form of aspergillosis. Aspergilloma is most often caused by Aspergillus fumigatus but several other species can also cause it. Surgical resection of the lesion is the most common and effective treatment.
The Aspergillis is actively growing through the tissues of the patient with a tendency to invade blood vessels. The infection typically starts in the lungs but may rapidly spread throughout the entire body and the mortality is very high. This form of aspergillosis occurs in patients who are severely immunocompromised and who have a serious underlying illness, such as a malignancy, or who are receiving cytotoxic or immunosuppressive therapy. Neutropaenia and prior treatment with corticosteroids are the most important common pre-disposing factors for the development of invasive aspergillosis. Patients with acute leukaemia and heart, liver or bone marrow transplant patients are at greatest risk of developing invasive aspergillosis. It has been estimated that 25 to 40% of such patients have invasive aspergillosis at post mortem. Aspergillus fumigatus is the species most frequently implicated.
The lung is the sole site of infection in 70% of patients with other organs becoming the site of dissemination in many cases. The target organ(s) for dissemination depends upon the underlying predisposing factor. There is widespread destructive growth of Aspergillus species in lung tissue and the fungus invades blood vessels where it causes thrombosis. Septic emboli may spread the infection to other organs especially the kidneys, heart and brain. Invasive aspergillosis has a poor prognosis and is often diagnosed post mortem.
BlastomycosisThe Blastomyces species include:
Cutaneous and systemic (disseminated) blastomycosis are the two clinical forms of the disease. Blastomycosis in general is acquired by inhalation and initially presents with a pulmonary infection which may later disseminate to other organs and systems. Primary cutaneous infection due to direct inoculation of the fungus into the skin is also likely. Hematogenous spread of the organism results in infection of skin, bones, kidneys and male urogenital system. Blastomycosis of the central nervous system (CNS), eyes, larynx, paranasal sinuses, tongue, adrenal glands, uterus, ovaries, gastrointestinal tract, liver and spleen have so far been reported. Otitis media, resulting in cranial osteomyelitis may also develop. Reactivation blastomycosis and subclinical, self-limited infections have been defined.
CandidiasisThere are about 154 species of Candida which cause candidiasis, keratitis, systemic infections and skin and nail infections in man. The more common ones include:
The genus Candida includes around 154 species. Among these, six are most frequently isolated in human infections. While Candida albicans (50%)is the most abundant and significant species, Candida tropicalis (15-30%), Candida glabrata (15-30%), Candida parapsilosis (15-30%), Candida krusei (up to 1%), and Candida lusitaniae (up to 1%) are also isolated as causative agents of Candida infections. Importantly, there has been a recent increase in infections due to non-albicans Candida, such as Candida glabrata and Candida krusei. Patients receiving fluconazole prophylaxis are particularly at risk of developing infections due to fluconazole-resistant Candida krusei and Candida glabrata strains. Nevertheless, the diversity of Candida that are encountered in infections is expanding and the emergence of other species that were rarely in play in the past is now likely.
Infections caused by Candida are in general referred to as candidiasis. The clinical spectrum of candidiasis is extremely diverse. Almost any organ or system in the body can be affected. Candidiasis may be superficial and local or deep-seated and disseminated. Disseminated infections arise from hematogenous spread from the primarily infected locus. Candida albicans is the most pathogenic and most commonly encountered species. Its ability to adhere to host tissues, produce secretory aspartyl proteases and phospholipase enzymes and transform from yeast to hyphal phase are the major determinants of its pathogenicity.
Mucosal candidiasis is a condition with pain, redness and sometimes a whitish coating or discharge of the mucosa of the mouth or vagina. The most common species of Candida causing problems is Candida albicans. Candida albicans is normally present in small numbers on the mucosa and problems arise when it overgrows. Oral canidiasis may occur in infants without any obvious predisposing factors. Candida may also contribute to rash in the diaper area in infants although chemical irritation from amonia is also important cause. Vaginal candidiasis may occur without obvious predisposing factors and some women have very frequent very troublesome vaginal candidiasis without apparent cause. With the possible exception of isolated episodes of mild oral candidiasis in an infant it is appropriate to consider in each case the possibility of an underlying cause.
Blood stream infection with Candida albicans and other species of Candida is becoming increasingly important in hospitalised patients. In many respects this reflects longer survival of and more interventions on people with conditions that formerly were rapidly fatal. It is well recognised that invasive Candida infection occurs in the profoundly immunocompromised patients such as those who have had bone marrow ablation or those who have received intensive cytotoxic chemotherapy for what ever reason. It is also a major problem in those with complex surgical problems. Invasive Candida infection is associated with prolonged neutropaenia, central lines, and total parenteral nutrition. Very importantly, invasive candidiasis is associated with prolonged administration of broad-spectrum antibacterial agents.
Probably the most common underlying cause is taking prescribed antibacterial agents. Administration of antibacterial agents disrupts the normal bacterial flora of the mucosa and may permit overgrowth of Candida albicans. The overgrowth is associated with mucositis. Candida mucositis is one of the very good reasons for persuading people not to take antibacterial agents for trivial infections. It is a good example to use in illustrating to people that antibacterial agents may do them more harm than good if taken without adequate reason. Other predisposing factors include pregnancy, oral contraceptives, diabetes mellitus, administration of corticosteroids, and of course cellular immunedeficiency. Mucosal candidiasis is a very frequent problem those receiving cytotoxic or other immunosuppresive therapy. Oro-pharyngeal or vaginal candidiasis is one of the early manifestations of AIDS and this should be considered at an early stage in those with very frequent or very sever mucosal candidiasis.
Some factors which are predisposing for Candida infections are mechanical damage such as burns, bruises or abrasions and local occlusion by dentures, medical dressings or tight clothing (especially in the obese). Nutritional factors include Avitaminosis, iron deficiency and general malnutrition; physiological factors include age extremes, pregnancy and menses. Some systemic illnesses such as Down's syndrome, acrodermatitis enteropathica, diabetes mellitus, Addison's disease, Cushing's syndrome, hypoadrenalism, hypothyroidism, hypoparathyroidism, uremia, malignancy and immunodeficiency conditions, HIV/AIDS increase the susceptibility to Candida infections. Medical factors include catheters, IV drug use, radiation, corticosteroids, immunosuppressive agents, broadspectrum antibiotics, tranquilizers, oral contraceptives, colchicine and phenylbutazone.
Thrush is a popular name for vaginal candidiasis which occurs deep inside the vagina. Most of the time it does no harm as it is kept in check by the natural acidic environment. But when this pH is upset, Candida can multiply and cause problems. The following factors can disturb the acid balance in the vagina and lead to an attack.
Candida albicans is a yeast which is pathogenic to people, in temperate climates primarily as a vaginal infection in women. It can be a health hazard in recreational waters, more so in tropical and sub-tropical climates, and also passed person to person especially during intercourse. It does not appear to reproduce in nature but can be isolated from crustaceans, molluscs, seagulls, pigeons, the skin of hospital patients, swimming pools and shower rooms. Australian surfers who suffer cuts and abrasions may become infected with Candida albicans. It is also responsible for oral, cutaneous, ocular, bronchial, urinary tract, pulmonary and vaginal infections called candidiasis. Specific concerns include oral thrush, venereal disease, endocarditis, cystic fibrosis, meningitis and paronchya. There are no definitive epidemiological studies linking infections with water levels of Candida albicans but women swimming at contaminated marine beaches have a higher instance of vaginal infections due to Candida albicans.
Vulvovaginal candidiasis, VVC, sometimes referred to as candidal vaginitis, monilial infection or vaginal yeast infection is a common cause of vaginal irritation. It has been estimated that approximately 75 percent of all women will experience at least one episode of VVC during their lifetime. VVC is caused by an overabundance or overgrowth of yeast cells, primarily Candida albicans, that normally colonize the vagina. The most frequent symptoms of VVC in women are itching, burning and irritation of the vagina. Painful urination and/or intercourse are common. Abnormal vaginal discharge is not always present and may be minimal. Most male partners of women with VVC do not experience any symptoms of the infection. However, a transient rash and burning sensation of the penis have been reported after intercourse if condoms were not used. These symptoms are usually self-limiting.
Systemic candidosis is now the most frequent cause of fungal infection in immunocompromised patients. Lesions in systemic candidosis may be localised in the urinary tract, liver, heart valves where they cause endocarditis, meninges where it may cause meningitis or peritoneal cavity. The infection may also be widely disseminated and associated with a septicaemia known as candidaemia. Deep-seated candidosis is difficult to diagnose and treat, and its prognosis is generally poor. Candida albicans accounts for most cases of systemic candidosis, but other species, most notably Candida tropicalis, are increasingly implicated as opportunistic pathogens.
Candida infections may manifest in various clinical forms depending on the underlying immunological status of the patient. Systemic candidosis occurs mainly as an opportunistic infection in patients in whom an underlying disease or its treatment result in yeast overgrowth and at the same time severely impair general resistance to infection. In patients with AIDS, for example, the most common clinical manifestation is oropharyngeal infection and oesophagitis. This may be accompanied by vaginitis, onychomycosis and paronychia. These infections rarely become disseminated although they may be recurrent.
Candidaemia is seen mainly in postoperative or immunosuppressed patients and is marked by an intermittent pyrexia. In some patients the candidaemia clears spontaneously or disappears when contaminated intravenous catheters are removed. Some patients with candidaemia, however, most notably those treated with cytotoxic drugs or corticosteroids, develop generalised or localised deep-seated infection. Disseminated candidosis is seen mainly in patients with acute leukaemia, and in certain groups of surgical patients. Common sites of involvement in disseminated infection include the kidney, liver, brain and gastrointestinal tract; pulmonary infections are rare. The occurrence of white candidal lesions within the eye-referred to as Candida endophthalmitis is one of the common signs of deep-seated candidosis.
Urinary tract infections due to Candida may affect the kidneys or may be localized in the bladder. Infection of the kidney is usually haematogenous in origin and ascending infection is thought to be rare. Bladder infections are usually associated with the presence of an indwelling urinary catheter, previous disease or surgery of the urinary tract, urinary stasis, diabetes mellitus or treatment with antibiotics. Candida infection of the urinary tract often clears spontaneously when the underlying cause is corrected.
Endogenous oculomycosis is an eye infection which results from fungal dissemination from another body site. Eye involvement is typically a terminal event following widespread dissemination. The mycosis may involve the orbit, retina, optic nerve, sclera, conjunctiva and adjacent tissue. The diseases in order of frequency are: candidiasis, cryptococcosis, cocciodiomycosis, blastomycosis, sporotrichosis, paracocciodiomycosis and histoplasmosis. The most common organism is Candida albicans.
ChromoblastomycosisSome species responsible for this disease include:
Cryptococcosis caused by the capsulated yeast Cryptococcus neoformans, is principally a disease of the central nervous system, although the primary site of infection is the lungs. It is from there that in a proportion of people the yeast disseminates, mostly affecting the meninges. Cryptococcosis occurs sporadically throughout the world. It is now seen most often in patients who have AIDS. Cryptococcus neoformans has been isolated from bird droppings thriving in aged pigeon droppings in soil or in avian nesting places, such as barns or window ledges and also grows in soil and even on eucalyptus trees. It is an environmental saprophytic yeast found worldwide. It is believed that human infection occurs after the organism is aerosolized and inhaled.
Cryptococcal meningitis can occur in individuals who appear otherwise healthy but occurs most frequently in patients with abnormalities of T lymphocyte function. These include patients with Hodgkin's disease, sarcoidosis, collagen disease and neoplasms. However, most cryptococcal infections are now seen in people with AIDS; about 10% of whom develop cryptococcosis.
A mild, self-limiting pulmonary infection is believed to be the commonest form of cryptococcosis and this represents the primary infection. In a proportion of patients, the disease will progress to a chronic meningitis or meningoencephalitis. This condition develops insidiously with headaches and low grade pyrexia. These symptoms are followed by changes in mental state, anorexia, visual disturbances and eventually coma then death. The course of the disease run for a few months to several years, but the outcome is always fatal unless it is treated. AIDS patients with cryptococcosis generally develop a chronic meningeal form and the symptoms tend to milder than in other patients. Although predominantly a disease of the central nervous system, lesions of the skin, mucosa, internal soft organs and bones may also occur. In its disseminated form the disease may resemble tuberculosis. Haematogenous spread affecting multiple organs occurs mainly in AIDS cases.
Cryptococcus neoformans has been recognized for many years as a pathogen that usually affects patients with depressed cell-mediated immunity. In the past, a small number of cases were reported annually, often in cancer or organ-transplant patients. However, the incidence of cryptococcosis has dramatically increased over the past 15 years, mainly in patients with AIDS. In a non-immunocompromised host, the fungus is usually attacked by polymorphonuclear leukocytes and macrophages. Phagocytosis is facilitated by the binding of complement, primarily C3. If the early immune response to infection is poor, as in HIV-infected persons, fungal replication is rapid and the fungal burden is increased. The fungus disseminates and has a strong predilection for the meninges, cerebro-spinal fluid (CSF) and brain. The cryptococci are neurotropic for several reasons, including the lack of a normal inflammatory response to the fungus in the brain and the absence of soluble anticryptococcal factors in CSF also serves as a good growth medium, with the neurotransmitter dopamine enhancing proliferation of C neoformans.
Cryptococcus neoformans infection is more common in patients with AIDS than in non-HIV-infected persons. The most common nonmeningeal site is pulmonary; the lungs are affected in 30% to 40% of patients, even though the respiratory system is the presumed portal of entry for the organism, pulmonary disease does not develop in the majority of patients. The outcome with pulmonary cryptococcosis is poor. Acute-phase mortality is 42% and median survival is about 23 weeks in patients who have disseminated disease. Other potential and reported sites of cryptococcal involvement include the skin, kidney, liver, pericardium, joints and adrenal glands. The prostate gland may provide sanctuary for and be a nidus for recurrent infection. Thus, cryptococcal disease in patients with AIDS is usually a systemic illness with a definite predilection for the central nervous system and, less commonly, the lungs. Even when patients are successfully treated for cryptococcal meningitis, they are at high risk for relapse. Retrospective studies have shown a relapse rate of 50% to 60% and a shorter life expectancy for patients not treated with suppressive therapy.
Recently, in August 2001, it was reported in the newspaper that in the last 30 months Cryptococcus neoformans has been responsible for 4 deaths on southeastern Vancouver Island and about 20 other non-fatal cases of infection in people with normal functioning immune systems. Pets, dogs and cats, and other animals, such as porpoises, have also been infected.
Most AIDS patients diagnosed with histoplasmosis (95%) have disseminated disease, They commonly are in a state of advanced immunosuppression. These patients usually present with nonspecific symptoms, eg, fever, weight loss, and fatigue, of 1 to 3 months' duration. Central nervous system disease, including meningitis, focal brain lesions and encephalitis, occurs in 10% to 20% of cases. Relapse is common after therapy for acute disease, and lifelong suppressive oral therapy is needed.
Before the appearance of HIV, approximately 95% of the cases reported of Histoplasmosis capsulati or North american histoplasmosis were in-apparent, sub-clinical, or benign and five percent of them where a chronic progressive lung disease with chronic cutaneous or systemic disease, or an acute fulminating fatal systemic disease. After the appearance of HIV the disease is almost always seen in HIV positive patients or other immunocompromised individuals. All stages of this disease may mimic tuberculosis. Histoplasmosis may coexist with actinomycosis, other mycoses, sarcoidosis or tuberculosis. The disease may be disseminated or pulmonary.
Histoplasmosis duboisii or African histoplasmosis is a mycotic infection primarily involving cutaneous, liver, lung, lymphatic, subcutaneous, and osseous tissues. Skin and bone are the most frequently invaded sites. The etiologic agent grows as a large yeast within the giant cells as well as small cells that are typical of those seen in histoplasmosis capsulati. Nodular and ulcerative cutaneous and osteolytic lesions of bone that disseminate or remain localized are the primary clinical characteristics of histoplasmosis duboisii. The disease may be disseminated or localized.
Mycotic keratitisA number of fungi are involved in this eye infection.
General risk factors for any type of onychomychosis are:
This is classically a disease affecting young people around the pubertal time probably related with hormonal changes and increase in sebum secretion. However, children are not excepted from suffering this fungal infection. Both males and females can be equally affected. High temperatures and humidity favor the occurrance of Pityriasis versicolor. Accordingly, tropical areas can have prevalence as high as 40% and the frequency is higher during summer months in temperate climates. The extension and severity of the lesions tends to be worse in tropical climates.
Malassezia furfur is not usually cultured since it is lipophilic. The yeast has also been isolated from blood cultures of neonates undergoing parenteral nutrition and from persons with IV catheters. The natural habitat of this fungus is man.
Cutaneous zygomycosis is caused by Conidiobolus. This infection is a chronic inflammatory or granulomatus disease that is typically restricted to the nasal sub-mucosa and characterized by polyps or palpable restricted subcutaneous masses. Symptoms include nasal swelling beginning in the inferior turbinates, which may extend to the foramina, ostia, paranasal sinuses, sub-mucosa, and sutures. The infections are typically bilateral, but may be unilateral. Masses may be disfiguring, palpable, and anchored to underlying structures. Epidermis may become acanthotic and erythematous. Eyelids may be swollen. X-rays show opaque antrum, obliteration of nasal air spaces, and mucosal thickening. Over 80% of the cases have been in males. The disease is relatively benign, sometimes clearing spontaneously. The infectious agent is a soil fungus.
Subcutaneous zygomycosis is a chronic inflammatory or granulomatous disease generally restricted to the limbs, chest, back, or buttocks and characterized by massive palpable, indurated, non-ulcerating subcutaneous masses. The disease is primarily in children with a predominance in males. The mycosis begins as a subcutaneous nodule. The swelling is firm, well circumscribed, painless with some pruritis. The mass is palpable and attached to the overlying skin, but not the underlying fascia. The skin is atrophic and discolored or hyperpigmented. The mass increases in size and may involve the entire arm, shoulder, upper body, face, neck, entire leg or buttocks, or both. Internal organs have been reported to be occasionally involved. Leukocytosis, up to 29,000, and eosinophilia, up to 30%, may be present. The prognosis is generally good and the gross disfigurement usually resolves. These are soil and dung fungi.
Zygomycosis is a disease caused by members of the Mucorales that is generally acute and rapidly developing in debilitated patients. The disease typically involves the rhino-facial-cranial area, lungs, gastrointestinal tract, skin, or less commonly other organ systems. The disease is associated with the acidotic diabetic, malnourished children, severely burned patients and other diseases such as leukemia and lymphoma, immunosuppressive therapy, or use of cytotoxins and corticosteroids. The fungi show a predilection for vessel (arterial) invasion resulting in embolization and necrosis of surrounding tissue. Suppurative pyogenic reactions develop. Infections are typically acute and fulminant. Rhinocerebral disease in acidotic patients usually results in death, often within a few days. The disease may be rhinocerebral, thoracic, abdominal-pelvic and gastric or cutaneous. The prognosis is grave, especially when the rhinocerebral area is involved in patients with uncontrolled diabetes. Most cases of gastric and pelvic disease are diagnosed at autopsy. Many cases occur in patients with pulmonary disease, leukemia, or with lymphomas. These are soil fungi.
Fungal Pathogens Species List
Descriptions of Fungal Pathogens
Absidia species are filamentous fungi that are cosmopolitan and ubiquitous in nature as common environmental contaminants. They are found in plant debris and soil, as well as being isolated from foods and indoor air environment. They often cause food spoilage. The genus Absidia currently contains 21 species. The most commonly isolated species is Absidia corymbifera. It is the only recognized pathogen among the other Absidia species. Some of the other Absidia species are Absidia coerulea, Absidia cylindrospora, Absidia glauca, and Absidia spinosa. Synonyms for Absidia corymbifera include Absidia ramosa and Mucor corymbifer.
Absidia corymbifera is a relatively rare cause of human zygomycosis. Zygomycosis is an opportunistic mycoses that manifests with pulmonary, rhinocerebral, cutaneous, gastrointestinal, renal or meningeal involvement. Disseminated zygomycosis may originate from these infections. Zygomycosis is very rarely observed in immunocompetent host. Absidia corymbifera is more commonly reported as an animal pathogen. It may cause mycotic abortion in the cow. Since Absidia are cosmopolitan and ubiquitous in nature, they are also common laboratory contaminants. Thus, their isolation in culture requires cautious evaluation. Nevertheless, the growth of Absidia, particularly from clinical samples of patients with immunosupression or diabetes mellitus, should be regarded as potentially significant. Also, the visualization of typical hyphae of zygomycetes group of fungi on direct microscopic examination, of particularly a sterile body site, should be considered significant even if the culture yields no growth.
Acremonium are filamentous, cosmopolitan fungi commonly isolated from plant debris and soil. The sexual state of Acremonium is not well-defined. Thus, it is classified among the deuteromycetes group of fungi by some authorities. Others prefer to include it in the Ascomycota phylum, due to its structural properties similar to those of that group.
There are three main species of Acremonium implicated in infections: Acremonium falciform, Acremonium kiliense, and Acremonium recifei. Acremonium is one of the causative agents of eumycotic white grain mycetoma. Rare cases of onychomycosis, keratitis, endophthalmitis, endocarditis, meningitis, peritonitis, and osteomyelitis due to Acremonium have also been reported. This fungus is known to cause opportunistic infections in immunocompromised patients, such as the bone marrow transplant recipients. Infections of artificial implants due to Acremonium are occasionally observed. Since Acremonium species are cosmopolitan in nature, they are often encountered as contaminants.
Its growth rate is variable. While some strains grow rapidly and reach a diameter of 3 to 9 cm after incubation at 25 degrees Celsius for 7 days on potato glucose agar, the others grow slowly reaching a colony diameter of only 0.5-1 cm in the specified conditions. The colonies are glabrous at the beginning and become downy, velvety or powdery by maturation. Radial ridges or folds may develop. The surface color is creamy white to pale yellow or tan. The reverse side is pale yellow to tan. The ability of Arthrographis to grow at 45 degrees Celsius is significant for its identification.
Arthrographis is a cosmopolitan filamentous fungus isolated from soil and compost. The genus Pithoascus is the telemorphic genus associated with Arthrographis. Two species of Arthrographis have been defined; Arthrographis cuboidea and Arthrographis kalrae. Arthrographis kalrae is the most commonly isolated Arthrographis species in clinical mycology laboratories. Arthrographis kalrae is among the causative agents of onychomycosis. Arthrographis have also been occasionally isolated from respiratory secretions of patients with chronic pulmonary disease. However, their pathogenic role in this specific clinical setting is unclear. Since Arthrographis species are cosmopolitan and ubiquitous in nature, they are also common laboratory contaminants. Thus, their isolation in culture requires cautious evaluation.
Aspergillus is a filamentous, cosmopolitan and ubiquitous fungus found in nature. It is commonly isolated from soil, plant debris, and indoor air environment. While the teleomorphic state has only been described for some of the Aspergillus, others are accepted to be mitosporic, without any known sexual spore production.
The genus Aspergillus includes over 185 species. Around 20 species have so far been reported as causative agents of opportunistic infections in man. Among these, Aspergillus fumigatus is the most commonly isolated species, followed by Aspergillus flavus and Aspergillus niger. Aspergillus clavatus, Aspergillus glaucus group, Aspergillus nidulans, Aspergillus oryzae, Aspergillus terreus, Aspergillus ustus and Aspergillus versicolor are among the other species less commonly isolated as opportunistic pathogens.
Aspergillus are well-known to play roles in three different clinical settings in man: opportunistic infections, allergic states and toxicoses. Immunosuppression is the major predisposing factor to development of opportunistic infections. These wide-ranging infections vary from local involvement to complete dissemination and as a whole are called aspergillosis. Among all filamentous fungi, Aspergillu is in general the most commonly isolated one in invasive infections. It is the second most commonly recovered fungus in opportunistic mycoses following Candida.
Almost any organ or system in human body may be involved. Onychomycosis, sinusitis, cerebral aspergillosis, meningitis, endocarditis, myocarditis, pulmonary aspergillosis, osteomyelitis, otomycosis, endophthalmitis, cutaneous aspergillosis, hepatosplenic aspergillosis, as well as Aspergillus fungemia, and disseminated aspergillosis may develop. Nosocomial occurence of aspergillosis due to catheters and other devices is also likely. Constructions in hospitals constitute a major risk for development of aspergillosis in particularly neutropenic patients.
Aspergillus may also be local colonizers in previously developed lung cavities due to tuberculosis, sarcoidosis, bronchiectasis, pneumoconiosis, ankylosing spondylitis or neoplasms, presenting as a distinct clinical entity, called aspergilloma. Aspergilloma may also occur in kidneys. Some Aspergillus antigens are fungal allergens and may initiate allergic bronchopulmonary aspergillosis particularly in atopic host. Some Aspergillus produce various mycotoxins. These mycotoxins, by chronic ingestion, have proven to possess carcinogenic potential particularly in animals. Among these mycotoxins, aflatoxin is well-known and may induce hepatocellular carcinoma. It is mostly produced by Aspergillus flavu and contaminates foodstuff, such as peanuts.
Aspergillus can cause infections in animals as well as in man. In birds, respiratory infections may develop due to Aspergillus. It may induce mycotic abortion in the cattle and the sheep. Ingestion of high amounts of aflatoxin may induce lethal effect in poultry animals fed with grain contaminated with the toxin. Since Aspergillus. are found in nature, they are also common laboratory contaminants.
Basidiobolu is a filamentous fungus isolated from dung of amphibians, reptiles and insectivorous bats, as well as wood lice, plant debris and soil. Although it is cosmopolitan, the human infections due to Basidiobolus are reported mostly from Africa, South America and tropical Asia. Although the pathogenic Basidiobolus isolates have once been identified as separate species, Basidiobolus ranarum, Basidiobolus meristosporus andBasidiobolus haptosporus, recent work on their antigens, restriction analysis of rDNA, and isoenzyme banding show that all Basidiobolu isolates that are pathogenic to human belong to a unique species, Basidiobolus ranarum.
Basidiobolus ranarum is the etiologic agent of subcutaneous chronic zygomycosis in man. This infection is also called entomophthoromycosis basidiobolae. It is characterized by its granulamatous nature and formation of hard, nonulcerating subcutaneous masses at limbs, chest, back, and buttocks. Systemic infection is rare. Basidiobolu is a true pathogen, causing infections in immunocompetent host. However, recent data on angioinvasive infections due to Basidiobolu in immunocompromised patients suggest that it is emerging as an opportunistic pathogen as well. It may rarely cause acute zygomycosis, which is similar to that defined for the zygomycetous fungi in the Mucorales order. Gastrointestinal infections due to Basidiobolus ranarum have also been reported in man. Basidiobolus can cause infections in animals as well as humans. Cutaneous lesions in amphibians, subcutaneous infection in horses and gastrointestinal lesions in dogs have so far been reported.
Bipolaris is a dermatiaceous, filamentous fungus. It is cosmopolitan in nature and is isolated from plant debris and soil. The pathogenic species have known teleomorphic states in the genus Cochliobolus and produce ascospores. The genus Bipolaris contains several species. Among these, three well-known pathogenic species are Bipolaris spicifera, Bipolaris australiensis, and Bipolaris hawaiiensis. Bipolaris is one of the causative agents of phaeohyphomycosis. The clinical spectrum is diverse, including allergic and chronic invasive sinusitis, keratitis, endophthalmitis, endocarditis, endarteritis, osteomyelitis, meningoencephalitis, peritonitis, otitis media (in agricultural field workers) and fungemia as well as cutaneous and pulmonary infections and allergic bronchopulmonary disease. Bipolaris can infect both immunocompetent and immunocompromised host As well as being isolated as saprophytes on plants, Bipolaris may be pathogenic to certain plant species, particularly to Gramineae and also to animals, such as the dog. It may cause nasal mycotic granuloma in the cattle. Bipolaris may also be isolated as a laboratory contaminant.
Blastomyces dermatitidis is a thermally dimorphic fungus and a probable saprobe of the soil. It is very rarely isolated from its natural habitat. Isolation from the environment is most likely when the sample contains soil and is rich in organic material such as animal feces, plant fragments, insect remains and dust. If the substrate is moist, lacks exposure to direct sunlight, contains organic debris, and has a pH of less than 6.0, isolation of Blastomyces dermatitidis is probable. It is endemic in North America. Missisipi, Ohio and Missouri valleys are the geographic locations with highest incidence of infections due to Blastomyces dermatitidis. African Blastomyces dermatitidi strains isolated from cases in Africa also exist. It was demonstrated that African type strains are not identical with the North American strains. These two groups most probably constitute two distinct serotypes of Blastomyces dermatitidis showing geographic diversity. They have common and varying antigens.
The sexual state (teleomorph) of Blastomyces dermatitidis belongs to the family Gymnoascaceae and is referred to as Ajellomyces dermatitidis. Ascospores are the sexual spores produced by this genus. Blastomyces dermatitidis is the only species included in the genus Blastomyces. It is the causative agent of blastomycosis which is one of the true systemic (endemic) mycoses. Although Blastomyces dermatitidis is a pathogenic fungus and blastomycosis occurs mainly in immunocompetent hosts, it may also effect immunocompromised patients, indicating that Blastomyces dermatitidis has now emerged as an opportunistic pathogen. Blastomyces dermatitidis can also infect dogs. Canine blastomycosis has a similar pathogenesis to human blastomycosis. Dogs are infected by inhaling the infectious particles. There is no evidence of animal to human transmission of the disease.
Colonies of Blastoschizomyces capitatus grow rapidly and mature in about 5 days. The texture of the colony is yeast-like, and white to cream colored. It becomes mould-like, wrinkled, and develops short aerial hyphae by aging. Blastoschizomyces capitatus can grow at 45 degrees Celsius. Blastoschizomyces is a yeast isolated from soil, beach sand, poultry feaces, and wood pulp. As well as being an environmental saprobe, it is found in normal microbial flora of human skin, and digestive and respiratory tracts.
The genus currently contains a single species, Blastoschizomyces capitatus. Synonyms include Blastoschizomyces pseudotrichosporon, Trichosporon capitatum and Geotrichum capitatum. Formerly known as Trichosporon capitatum and classified in Basidiomycetes, this fungus was later found to be more closely related to Ascomycetes based on its cell wall structure, septal pores, G+C content, and production of numerous arthroconidia and few blastoconidia. Its telemorph Dipodascus capitatu producing ascospores was then discovered, strengthening its classification in class Ascomycetes. Prior to its transfer to the new genus, Blastoschizomyces, this fungus was included in genus Geotrichum. However, its property to produce annelloconidia as well as arthroconidia leaded to general acceptance of its classification in a new genus, Blastoschizomyce.
Blastoschizomyces capitatus is an emerging opportunistic fungus potentially pathogenic in cases of immunosupression. Neutropenic patients, as well as those receiving chemotherapy, corticosteroids or antibiotics are at risk. Surgery, drug abuse, catheters, and low dose azole treatment have also been reported as predisposing factors. Clinical manifestations of Blastoschizomyces capitatus infections are diverse. Immunocompetent hosts may also develop Blastoschizomyces capitatus infections. Onychomycosis has been reported in an otherwise healthy individual. Infusion of intravenous fluids contaminated with Blastoschizomyces capitatu was been ultimately fatal in a six-month old infant who had no proven immunosupression. Fungemia and disseminated infections are likely in immunocompromised hosts. The lungs, kidneys, liver, spleen, brain and endocardium may be involved. Endocarditis, osteomyelitis, meningitis, encephalitis, urinary tract infection, mycetoma and pneumothorax may develop.
The colonies of Candida are cream colored to yellowish, grow rapidly and mature in 3 days. The texture of the colony may be pasty, smooth, glistening or dry, wrinkled and dull, depending on the species. The microscopic features of Candida also show species-related variations. All species produce blastoconidia singly or in small clusters. Blastoconidia may be round or elongate. Most species produce pseudohyphae which may be long, branched or curved. True hyphae and chlamydospores are produced by strains of some Candida. Although they are the members of the same genus, the various species do have some degree of unique behavior with respect to their colony texture at 25 degrees Celsius and fermentation or assimilation profiles in biochemical tests.
Candida should be differentiated from other clinically encountered yeasts, such as Blastoschizomyces, Cryptococcus, Geotrichum, Malassezia, Rhodotorula, Saccharomyces and Trichosporon. Morphology, capsule production, urease activity, ability to grow in presence of cycloheximide, growth pattern in Sabouraud broth and fermentation assimilation profiles help in differentiation of Candida from other yeasts. Well-developed pseudohyphae and one-celled blastoconidia characterize the common species of Candida. Candida differs from Cryptococcus by having well-developed pseudohyphae. The lack of arthroconidia is the major microscopic feature which differentiates Candida from Trichosporon and Geotrichum, the two genera that produce abundant arthroconidia.
Colonies are extremely variable and rapid growing, typically glabrous and grayish, later becoming white and cottony. With age, colonies become tan to brown in color at 25 degrees Celcius. Fertile hyphae usually arise at right angles to the vegetative hyphae, which are smaller in diameter. Arthroconidia are hyaline, 1-celled, rectangular to barrel shaped, alternating with empty disjunctor cells. Upon release by breakage of the disjunctor cells, the conidia have annular frills at both ends. At 37-40 Celcius, large spherules containing endospores form on special media. Coccidioides immitis can be recognized by the formation of alternating, hyaline arthroconidia in culture at 25-30 Celcius, and by the formation of spherules containing endospores in tissue or at elevated temperatures on special media. Coccidioides differ from Malbranchea by forming spherules containing endospores under the appropriate conditions. A specific and sensitive DNA probe and a exoantigen serologic procedure is available for the identification of cultures of Coccidioides immitis. Coccidioides immitis is an extremely dangerous fungus. It must be handled only in a biological safety cabinet.
Cryptococcus is an encapsulated yeast. Following its first identification in nature from peach juice samples, the major environmental sources of Cryptococcus neoformans have been shown to be either soil contaminated with pigeon droppings, Cryptococcus neoformans var. neoformans or eucalypus trees and decaying wood hollows in living trees, Cryptococcus neoformans var. gatti. Cryptococcus neoformans var. gattii was also isolated from goats with pulmonary disease. The genus Cryptococcus includes around 37 species. Of these, Cryptococcus neoforman is the only species that is pathogenic. It has four serotypes. Cryptococcus neoformans was generally accepted to include two varieties; var. gattii and var. neoformans. Until recently and traditionally, serotypes A and D were included in var. neoformans while serotypes B and D were included in var. gattii. However, in addition to the previously observed phenotypic differences, recent molecular studies have detected significant genetic variations between the two serotypes. Thus, it was recently proposed that a new variety, var. grubii, be created to contain serotype A . This leaves serotype D as the sole serotype in var. neoformans. The two varieties, neoforman and gattii are morphologically similar, except that basidiospores of var. neoformans are round and those of var. gattii are more elliptical in shape. The definitive identification of the two varieties is possible by biochemical tests, such as resistance to canavanine, use of glycine as the sole carbon and nitrogen source, and resistance of their urease enzymes to EDTA.
Among the other Cryptococcus species are Cryptococcus albidus, Cryptococcus laurentii, Cryptococcus terreus, Cryptococcus uniguttulatus, Cryptococcus luteolus and Cryptococcus gastricus. The telemorphic (sexual) reproductive phase of Cryptococcus that occurs in nature constitutes the genus Filobasidiella. If the strains of serotypes A or D mate with each other, Filobasidiella neoformans var. neoformans is the telemorph. Similarly, the mating of serotypes B or C forms the telemorph called Filobasidiella neformans var. bacillispora
Cryptococcus neoformans is the causative agent of cryptococcosis. Given the neurotropic nature of the fungus, the most common clinical form of cryptococcosis is meningoencephalitis. The course of the infection is usually subacute or chronic. Cryptococcosis may also involve the skin, lungs, prostate gland, urinary tract, eyes, myocardium, bones, and joints. The most commonly encountered predisposing factor for development of cryptococcosis is AIDS. Less commonly, organ transplant recipients or cancer patients receiving chemotherapeutics or long-term corticosteroid treatment may develop cryptococcosis. The polysaccharide capsule and phenol oxidase enzyme of Cryptococcus neoformans, as well as its ability to grow at 37 Celcous, are its major virulence factors. Recent data suggest that phospholipase enzymes may also play role as one of the potential virulence factors. The infection commonly starts following inhalation of the yeasts. Phenol oxidase enzyme functions in production of melanin. The melanizing enzyme presumably prevents formation of toxic hydroxy radicals and thus protects the fungal cell from oxidative stress as well as the immune defense mechanisms of the host.
In the August 30, 2001 Victoria Times-Colonist Newspaper it was reported that during the preceeding 30 months, four people with normal functioning immune systems had died of Cryptococcus neoformans infections and 20 others had become clinically infected. All cases occurred in the southeastern Vancouver Island coastal strip. Pets (cats and dogs) and other animals including porpoises, were also infected with this fungus.
Colonies are rapid growing, woolly, at first white, becoming dark olive green to black in color with a darkly pigmented reverse. Conidiophores are geniculate, septate, brown, branched or simple, solitary or in clusters, and sympodial. Conidia are several celled, pale brown to dark brown, with end cells lighter in color than central cells. The conidia typically are curved with an enlarged central cell, occasionally straight or pyriform, with a dark basal protuberant hilum. Species of Curvularia produce geniculate, dark, sympodial conidiophores that bear curved, multicelled, brown conidia that have their end cells lighter in color than the central cell (the latter typically is the largest cell). Curvularia is readily distinguished from Bipolaris by the fact that it has curved conidia with an enlarged central cell.
Epidermophyton colonies are slow growing, powdery and membranous, velvety, becoming woolly to suede-like, gently folded, khaki to olivaceous, pale yellow tan to deep yellow brown reverse. The colonies quickly become downy and sterile. Conidia are thin walled, 3- to 5- celled, smooth, clavate, single or in clusters. Microconidia are absent. Chlamydoconidia are common in older cultures. In vitro hair perforation test is negative. Isolates of Epidermophyton floccosum are slow growing, velvety, khaki to olivaceous or yellow green, becoming suede-like and furrowed with age. They produce abundant, smooth-walled, 3- to 5- celled, clavate conidia that occur typically in clusters. Epidermophyton floccosum differs from Epidermophyton stockdaleae by being unable to perforate hair. Only Epidermophyton floccosum is pathogenic.
Exophiala colonies are slow to rapid growing, usually moist and yeast-like initially, becoming woolly with age, olivaceous gray to black in color. Annellides are cylindrical to flask shaped, tapering toward their apices, on hyphalike conidiophores, integrated within the hyphae, as yeast-like cells, or any combination. Conidia are 1-celled, several-celled in Exophiala salmonis, hyaline to pale brown, accumulating as a ball at the apex of the annellide. Species of Exophiala are recognized by their cylindrical to lageniform annellides with balls of conidia at their apices. Exophiala species differ from members of the genera Phialophora and Wangiell by forming annellides rather than phialides. Some of the species have synamorphic forms in the genera Cladosporium, Phialophora, Rhinocladiella, Phaeococcomyce and Phaeoannellomyces. Many synonyms have been applied to the species including Torula, Phialophora and Sporotrichum. Some species include Exophiala jeanselmei, Exophiala spinifera, Exophiala salmonis, Exophila pisciphila, Exophiala castellanii and Exophiala dopicola.
Colonies are slow to moderately rapid growing, flat to raised and folded, often brittle, velvety to cottony, olivaceous black in color. Conidiophores are pale brown, erect, septate, sympodial with conidiogenous zones confined to the upper portion. Conidia are 1-celled, arising upon swollen denticles. Primary conidia function as sympodial conidiogenous cells, becoming irregularly swollen at their apices, giving rise to 1-celled, pale brown, secondary conidia on swollen denticles. Secondary conidia often produce tertiary series of conidia like those formed by the primary conidia, resulting in a complex conidial head. Other types of associated conidia may include branching chains of dematiaceous conidia like those formed by the genus Cladosporium, dematiaceous phialides having collarettes like those produced by the genus Phialophora, and sympodial conidiophores bearing 1-celled, pale brown conidia like those seen in the genus Rhinocladiella. Fonsecaea is recognized by its complex conidial head consisting of apically, irregularly swollen, series of conidia that function as conidiogenous cells. This type of development distinguishes Fonsecaea from Rhinocladiella, which produces a single row of 1-celled conidia around its conidiophore. Fonsecaea compacta differs from Fonsecaea pedrosoi by having subglobose to globose conidia occurring in compact heads, in contrast to the loose heads consisting of elongated conidia in Fonsecaea pedrosoi. Handle with care in a biological safety cabinet.
Colonies are rapid growing, woolly to cottony, flat, spreading, white, cream, tan, cinnamon, yellow, red to violet, or purple. Phialides are cylindrical, with a small collarette, solitary or as a component of a complex branching system. Macroconidia are 2- or more celled, smooth, cylindrical to curved, with a distinct basal foot cell, and tend to accumulate in balls or rafts. Microconidia are 1-celled (occasionally 2-celled), smooth, hyaline, ovoid to cylindrical, accumulating in balls (occasionally occurring in chains). Sporodochia are usually absent in culture. Members of the genus Fusarium produce sickle-shaped, multicelled macroconidia with foot cells. Fusarium differs from Cylindrocarpon by having macroconidia with foot cells and pointed distal ends; it differs from Acremonium by having macroconidia.
Colonies are rapid growing, dry, powdery to cottony (becoming yeastlike or slimy when the colony surface is disturbed), white in color. Conidiophores are absent. Arthroconidia are 1-celled, in chains, hyaline, and result from the fragmentation of undifferentiated hyphae by fission through double septa. The genus Geotrichum is characterized by chains of hyaline arthroconidia developing from undifferentiated hyphae that are released by fission through double septa. Geotrichum differs from Scytalidium by having hyaline arthroconidia; from Arthrographis and Oidiodendron by lacking conidiophores; from Malbranchea by having fission arthroconidia rather than arthroconidia released by disjunctor cells; and from Trichosporon and Moniliella by lacking blastoconidia. Geotrichum contains two species of medical interest: Geotrichium candidum and Geotrichium penicillatum.
Histoplasma is a thermally dimorphic fungus found in nature. Soil contaminated with bird droppings or excrements of bats is the common natural habitat for Histoplasma. Although it is claimed to exist worldwide, tropical areas are where this fungus is more frequently encountered. It is endemic in the Tennessee-Ohio-Missisipi river basins. The genus Histoplasma contains one species, Histoplasma capsulatum. Histoplasma capsulatum has two varieties; Histoplasma capsulatum var. capsulatum and Histoplasma capsulatum var. duboisii. It has a telemorph referred to as Ajellomyces capsulatus.
Histoplasma capsulatum is the causative agent of a true systemic (endemic) mycoses, called histoplasmosis. The spectrum of the disease is wide, varying from an acute benign pulmonary infection to a chronic pulmonary or fatal disseminated disease. Following acquisition of the conidia by inhalation, lungs are primarily involved. In case of dissemination of Histoplasma capsulatum var. capsulatum infection, reticuloendothelial system (RES) is most frequently involved. The fungus resides intracellularly in RES cells. Histoplasma capsulatum may also rarely involve the thyroid glands and may be isolated in fungemia. Unlike var. capsulatum, var. duboisii rarely involves the lungs but commonly involves the bones and skin. Var. duboisii is the causative agent of African histoplasmosis. Given the true systemic nature of histoplasmosis, otherwise healthy individuals are affected. However, dissemination and fatal course are more common in immunocompromised and elderly. Chronic cavitary histoplasmosis is most commonly observed in individuals with underlying pulmonary disease.
Lacazia is a yeast-like fungus that causes infection in humans, Homo sapiens and bottle-nosed dolphins, Tursiops truncatus. Aqueous environment appears to be mandatory for the life cycle of Lacazia. It is saprophytic in water and is transmitted to the vulnerable host via contact. Infections due to Lacazia are mostly reported from tropical zones. The genus Lacazia contains a single species, Lacazia loboi. The name Loboa loboi is still frequently used to refer to the causative agent of lobomycosis. Lacazia loboi is the causative agent of a tropical mycoses, lobomycosis, which is characterized by mucocutaneous lesions, that are usually nodular, vegetating, verrucous, cauliflower-like and hyper- or hypo-pigmented. Lower extremities and the ears are most commonly involved. Nasal and labial lesions have rarely been reported.
Aquarium employees and farmers constitute most of the cases with lobomycosis. Occupations such as gold-mining, fishing and hunting also predispose to Lacazia loboi infections. A previous cutaneous trauma, insect bite or wound cut enhance the entry of the fungus through the skin via contact with infected surrounding, such as dolphins. There is no evidence of person-to-person transmission of lobomycosis.
Colonies are variable, slow growing, raised to heaped, sometimes radially folded, woolly, and olivaceous to dark gray, yellow, or brown in color, sometimes producing a brownish diffusible pigment. Colonies are sterile, but sclerotia may be formed. Isolates of Madurella are recovered from cases of black-grained eumycetoma. In the laboratory they are dematiaceous and sterile. Under some conditions, occasional isolates of Madurella mycetomatis form phialides having collarettes. Madurella mycetomatis grows well at 37 Celcius; Madurella grisea does not.
Colonies are slow to rapid growing, glabrous to cottony, white to brightly covered. Conidiophores are hyphalike. Macroconidia are 2- to several-celled, thin to thick-walled, echinulate to roughened, solitary, obovoid in one species, typically spindle shaped, hyaline, often with an annular frill. Microconidia are 1-celled, smooth, thin walled, hyaline, ovoid to clavate, solitary. Isolates of Microsporum produce macroconidia that are spindle shaped to elliptic, thin to thick walled, echinulate to roughened. These isolates also produce 1-celled, smooth, hyaline, ovoid to clavate microconidia. Microsporum differs from Trichophyton and Epidermophyton by having echinulate to roughened macroconidia.
Colonies are slow growing, woolly, compact, folded, gray to brown with a dark brown reverse color. Ascostromata are without ostioles and are black, carbonaceous, and globose to ellipsoidal. Asci are in the center of the ascostromata, they are globose, or subglobose to clavate, thick walled, bitunicate, and contain 8 ascospores. Ascospores are 2-celled with a single transverse septum that is sharply constricted, ellipsoid, variable in size, dark brown, and smooth. Neotestudina is characterized by producing ascostromata composed of plates of radiating cells, globose to subglobose asci, and smooth, evenly pigmented ascospores with a germ pore at each end.
Paracoccidioides is a thermally dimorphic fungus. Although it has been isolated from soil and digestive tract of some animals, its natural habitat remains unknown. It mostly resides in soil which is humid and rich in proteins. It has been cultivated from fruit bats and armadillos. While the epidemiology of the infections due to Paracoccidioides has not been fully clarified, most infections with Paracoccidioides have been reported from Central and South America, particularly from Brazil, Venezuela, and Colombia. Geographic discrimination of the strains have recently been possible by randomly amplified polymorphic DNA analysis. The genus Paracoccidioides contains one species, Paracoccidioides brasiliensis. It is a mitosporic fungus and has no known telemorph.
Paracoccidioides brasiliensis is the causative agent of a true systemic (endemic) mycoses, called paracoccidioidomycosis. The spectrum of the disease is wide, varying from an asymptomatic infection verified by the skin test to a subclinical, symptomatic or chronic infection. Diagnosis of paracoccidioidomycosis is often difficult. The infection may become apparent several years after exposure to Paracoccidioides brasiliensis, suggesting the possibility of a long latent period. The infection is presumably acquired via inhalation of the conidia, followed by primary infection of the lungs. The degree of pathogenicity may vary and appears strain-dependent. An exocellular serine-thiol proteinase enzyme is a significant virulence factor of the fungus for tissue invasion. In addition to the primary pulmonary form of the disease, acute pulmonary, chronic pulmonary, and disseminated forms may also be observed. In case of disseminated paracoccidioidomycosis, reticuloendothelial system, skin and mucous membranes are frequently involved. Lymph nodes may also be infected during the course of the infection. Aortitis may develop. Given the true systemic nature of paracoccidioidomycosis, otherwise healthy individuals are affected. Acute pulmonary and disseminated paracoccidioidomycosis may rarely develop in immunocompromised host.
Colonies are moderately rapid growing, woolly to cottony, gray, gray brown to almost black, with a reverse color of iron gray to black. Conidiophores when present are short and hyphalike. Phialides are cylindrical to flask shaped, with collarettes, solitary or in clusters, along hyphae or on conidiophores, dematiaccous. Conidia are 1-celled, hyaline to brown, smooth, ovoid to cylindrical, occurring as a ball at the apex of the phialide. Balls of 1-celled conidia accumulating at the apices of dematiaceous phialides that are usually flask shaped with a distinct collarette characterize the more common species of Phialophora. Phialophora differs from Exophiala by having phialides; it differs from Wangiella by having phialides with collarettes.
Colonies are slow growing, small, folded, velvety and dark brown to black in color. Ascostromata are subglobose to irregular in shape and are black. Asci are ellipsoid, solitary or in clusters, with 8 ascospores and ascus walls that readily dissolve. Ascospores are 1-celled, fusoid, curved, and tapering toward both ends to form whiplike extensions; they are hyaline to darkly pigmented. Piedraia forms 1-celled, curved, tapering ascospores with an appendage at each end.
Colonies are rapid growing, spreading, cottony, at first white, becoming pale smoky brown in color. Cleistothecia form just beneath the agar surface and are globose, light brown to black, without appendages and without ostioles. Asci are subglobose to globose with 8 ascospores; ascus walls readily dissolve to release ascospores. Ascospores are 1 -celled, ovoid to ellipsoid, smooth, pale yellow brown to copper in color. Graphium, Scedosporium, or both forms may be present in the same isolate. Globose, black cleistothecia forming beneath the agar and having I-celled, ovoid, yellow brown to copper-colored ascospores are typical of the genus Pseudallescheria. Pseudallescheria differs from Petriella by forming nonostiolate cleistothecia. Petriellidium is a later synonym of Pseudallescheria.
Colonies are moderately rapid growing, flat, woolly to cottony, at first white. becoming olivaceous green to olivaceous gray in color with a dark reverse. Pycnidia are globose to flask shaped, ostiolate, membranous to carbonaceous, brown to black, with setae arisin from the upper portion of the pycnidia. Phialides arise from the inner lining of the pycnidia. Conidia are 1-celled, oval to cylindrical, hyaline, and may be slightly curved. Pyrenochaeta species form dark, ostiolate pycnidia having black setae arising from the upper portion of the pycnidia, and form 1 celled, oval to cylindrical conidia. Pyrenochaeta differs from Phoma by having setae.
Colonies are rapid growing, often filling the Petri dish, cottony and dense, at first white, becoming brownish gray in color. Sporangiophores are dark, solitary or in clusters, arising opposite rhizoids at a node. Sporangia are globose with flattened bases. Columellae are hemispherical. Sporangiospores are 1-celled, globose to ovoid, hyaline to brown, smooth or striated. Rhizopus species form globose sporangia on simple sporangiophores that arise opposite rhizoids at the nodes of the stolons. Rhizopus differs from Absidia, Mucor, and Rhizomucor by having simple sporangiophores arising opposite rhizoids at nodes.
Colonies are rapid growing, smooth, glistening or dull, sometimes roughened, soft, mucoid, cream to pink or coral red in color. Pseudohyphae are absent or rudimentary. Hyphae are absent. Blastoconidia are 1-celled, globose to elongate, typically with a capsule. Inositol assimilation is negative, fermentation of sugars is absent, and urease is produced. Rhodotorula forms pink to coral red colonies having globose to elongate, encapsulated cells, an inability to assimilate inositol or to ferment sugars, and the absence of pseudohyphae.Rhodotorula differs from Cryptococcus by not being able to assimilate inositol; it differs from Candida by producing pink to red colonies and and lacking pseudohyphae. Some species have teleomorphic genera in Rhodosporidium. There are about 22 species, common ones include Rhodotorula glutinis, Rhodotorula minuta and Rhodotorula mucilaginosa. Rhodotorula is a very rare pathogen, reported in a endocarditis case and in a meningitis case.
Colonies are rapid growing, flat, smooth, glistening or dull, and cream to tannish cream in color. Pseudohyphae may be present; when present, they are rudimentary. Hyphe are absent. Blastoconidia are 1-celled, globose, and ellipsoid to elongate. Asci contain 1 to 4 ascospores, and do not rupture at maturity. Ascospores often are globose. Nitrate is not utilized. Fermentation is positive. Typically the common isolates of Saccharomyces have asci containing 1 to 4 ascospores, the inability to utilize nitrate for growth, and 1-celled, multipolar blastoconidia. There are about 7 species, the most common one is Saccharomyces cerevisiae. The natural habitats are people, mammals, birds, the environment and plants.
Colonies are rapid growing, spreading, cottony, at first white, becoming pale smoky brown. Conidiophores are short or long, hypha-like. Conidiogenous cells are cylindrical annellides. Conidia are 1-celled, solitary or in balls, subglobose to elongate, smooth hyaline to pale brown. Graphium, Pseudallescheria, or both forms may be present. Scedosporium isolates form 1 -celled, brownish conidia that arise solitarily on hyphalike conidiophores, in clusters at the apices of annellides, or in both ways. Scedosporium apiospermum, previously known as Monosporium apiospermum, is often referred to by its sexual form name Pseudallescheria boydii. Scedosporium prolificans is the second pathogen in the genus Scedosporium, for which a sexual form is unknown.
Colonies are moderately rapid growing, granular to powdery, initially white, becoming light brown or buff tan, reverse color usually is tan. Conidiophores are hyphae-like and simple or branched. Annellides are solitary, in clusters, or form a penicillus; they are cylindrical and slightly swollen. Conidia are 1-celled, globose to pyriform, smooth, but more commonly rough walled, truncate, forming basipetal chains. A Trichurus anamorph (synnemata) may be present.
Isolates of Scopulariopsis brevicaulis are granular to powdery, light brown to buff tan, and form cylindrical annellides and chains of 1-celled, rough-walled conidia having truncate bases. Scopulariposis brumptii forms dark colored colonies. Scopulariopsis candida is another species. Scopulariopsis differs from Penicillium by forming annellides.
Colonies are rapid growing, moist, wrinkled, leathery to velvety in texture, at first white, becoming cream to dark brown or black at 25 Celsius. Conidiophores typically are present and are hypha-like, hyaline, septate, sympodial, and often have an inflated apex. Conidia are of two kinds: the first kind are 1-celled, globose to clavate, arise solitarily on slender denticles, often forming rosettes; the second kind are 1-celled, thick-walled, dematiaceous, and arise along the hyphae. Sporothrix schenckii is dimorphic and develops a yeast form at 37 Celsius. Sporothrix schenckii is recognized by its dimorphic nature. At 25 Celsius, it forms sympodial conidiophores having 1-celled hyaline conidia on denticles that frequently occur as rosettes at the apices of swollen condiophores, and dematiaceous 1-celled conidia along the hyphae. The latter conidia arre typically present only in fresh isolated strains. At 37 Celsiu, the fungus grows as a yeast.
Colonies are slow to rapid growing, waxy, glabrous to cottony, white to brightly colored. Conidiophores are hypha-like. Macroconidia are 2- or more-celled, generally thin-walled, in some species thick-walled, occasionally rare or absent, smooth, solitary, cylindrical, or clavate to cigar shaped. Microconidia are 1-celled, smooth, thin-walled, hyaline, ovoid to clavate, solitary or in clusters. The microconidia are often the predominant type of conidia. Macroconidia that are cylindrical, clavate to cigar shaped, thin or thick-walled, smooth, and ovoid to clavate are characteristic of the genus Trichophyton. Trichophyton differs from Microsporum and Epidermophyton by having cylindrical, clavate to cigar-shaped, thin-walled or thick-walled, smooth macroconidia.
Trichosporon is a yeast isolated from soil, water samples, vegetables, mammals, and birds. As well as being a member of the normal flora of mouth, skin and nails, it is the causative agent of superficial and deep infections in humans. The genus Trichosporon is non- or weakly fermentative. There is no sexual reproduction phase, but the fungus has a basidiomycetous affinity.
Trichosporon beigelii is the most significant pathogen in the genus Trichosporon. The name Trichosporon cutaneum has been often synonymously used with Trichosporon beigelii. There are some recent classification and nomenclature revisions of Trichosporon based on analysis of 26S rRNA sequences. There are also approaches other than molecular techniques to differentiate the newly named species from each other. The revised taxonomy results in 17 species and five varieties. Six of the of species are associated with infections in humans. Among the species causing human diseases are Trichosporon cutaneum. The name Trichosporon beigelii was excluded and Trichosporon cutaneum was retained. The other five newly named species in this revised classification are Trichosporon asteroides, Trichosporon ovoides, Trichosporon inkin, Trichosporon asahii and Trichosporon mucoides. Infections associated with each of these species have been described. In addition to the newly defined species and varieties, four serotypes of Trichosporon, I, II, III, and I-III, have been designated. While serotypes I, Trichosporon cutaneum and Trichosporon mucoides and II, Trichosporon asahii, Trichosporon asteroides, Trichosporon inkin and Trichosporon ovoides included pathogenic species, serotypes III and I-III are not causative agents of infection.
Other species of Trichosporon include Trichosporon brassicae, Trichosporon coremiformis, Trichosporon dulcitum, Trichosporon faecalis, Trichosporon gracile, Trichosporon jirovecii, Trichosporon lowideri, Trichosporon montevidense, Trichosporon muwides, Trichosporon paehachi, Trichosporon pullulans and Trichosporon sporotrichoides.
Trichosporon species are the causative agents of white piedra, superficial infections and invasive trichosporonosis. This fungus has emerged as an opportunistic fungal pathogen. Immunocompromised hosts are particularly under risk to develop invasive infection, which usually progresses rapidly, involving various organs and systems, including the lungs, kidneys, and spleen. Cutaneous lesions as a manifestation of disseminated infection are also likely. Trichosporon is one of the fungi isolated from patients with fungemia. It may infect prosthetic valves, central nervous system (including chronic meningitis), cornea and the peritoneum (in pateints receiving peritoneal dialysis). Benign funguria due to Trichosporon may be observed in renal transplant patients. Disseminated trichosporonosis in immunocompetent hosts is very rare.
Trichosporon cutaneum and Trichosporon asteroides cause superficial cutaneous infections; Trichosporon ovoides and Trichosporon inkin cause white piedra of the scalp and pubic hairs, respectively; Trichosporon asahii and Trichosporon mucoides cause systemic trichosporonosis.
Drinking WaterFungi are not generally problems in drinking water but may be problems if the potable water supplied is used for bathing, swimming pools, hot tubs and other recreational activities either as a liquid or as an aerosol. These exposures are covered below. Children playing in the sprinkler are exposed to aerosols which may contain fungi and breathe them into their lungs; one of the favoured locations for a systemic fungal infection to get started. Water used in hospitals to wash burns, flush eyes, mix solutions and other uses where it will come in contact with injured or damaged tissues should be sterile. Any water used for people with compromised immune systems must also be sterile since pathogenic fungi are a serious risk for such people.
RecreationA day at a water park is often followed by days of itching, swelling and pain in one or both ears. The common condition can develop when water is trapped inside your ear canals. Water in your ears provides the perfect environment for bacteria and fungi to grow. When that happens you can develop the symptoms of swimmer's ear. Swimmer's ear is an infection of the outer ear canal. The hallmark of swimmer's ear is redness and tenderness when pressing on the structure, right at the front part of the ear canal opening. For most cases of swimmer's ear, over-the-counter ear drops will dry up the ear canal and kill bacteria or fungi. Or you can use isopropyl alcohol, also known as rubbing alcohol. Place a small amount in the ear canal with an ear dropper after swimming. Put the alcohol in and then let it run right back out. That will get the water out of the ear and help prevent swimmer's ear. In rare cases, swimmer's ear can start off as a simple infection, but soon become a serious condition if not treated. In someone with diabetes, if left untreated, the infection can spread into the bone of the surrounding skull. Chronic swimmer's ear can be prevented by wearing ear plugs. But after the plugs are taken out, it's still a good idea to put in ear drops.
With few exceptions, veterinary and human mycology deal with the same fungal pathogens. Veterinary medical mycology deals with fungal disease in both invertebrate and vertebrate animals. Invertebrate fungal infections are typically dealt with on an individual basis by mycologists working with other specialists. Because fungal infections involving invertebrate animals are unusual, classical mycologists are typically needed to assist with the identification of the pathogenic fungus. In fact, the first reported animal disease was the fungus Beauvera bassiana that nearly destroyed the silk industry in China by attacking silk worms.
When fungi are suspected to cause animal disease, having criteria to distinguish infection, colonization and contamination is important in reaching a diagnosis. Unlike people, animals are typically covered over their entire body with large amounts of hair, or feathers in the case of birds. They are frequently contaminated with a variety of fungi that may or may not be causing the disease that is present. The same criteria used for human infections must be applied.
In domesticated animals, the same anti-fungal agents that are used to treat fungal disease in humans are used to treat their infections. There are exceptions; for example aquatic animals such as fish are treated differently. Some of the more common infections of the skin and tails are caused by organisms no longer considered to be fungi, e.g., Saprolegnia.
The interaction between plant pathogenic fungi and their host plants is extremely complex and should be viewed from the perspectives of both the fungus and the plant. The biology of pathogenic fungus that needs to be understood include factors such as how the fungus reproduces and if alternate hosts or special over wintering conditions are necessary. Other factors include the means by which the fungus reaches the host, such as water, wind, insect vectors like beetles (which carry the conidia of Ophiostoma ulmi which causes Dutch elm disease) or inappropriate storage conditions where the fungus can remain until a new crop is stored. These are examples of potential points to stop the spread of pathogenic fungi.
From the perspective of the host plant, its physiology and metabolism must be understood. Mineral nutrient requirements and ion uptake, water conditions like water related stress, internal transport processes for the manufacture and distribution of nutrients, the role of plant hormones, inhibitors, and phytochromes in the regulation of plant growth and development, must be understood. The effects of the physical environment where the plant is growing and how this impacts the plant's growth, development, and the correlation of biochemical changes that are occurring within the plant is likewise important. Some fungus-plant interactions are exceptionally specific. For example, the wheat rust fungus Puccinia graminis is classified into different races based upon how the genetic systems of the rust interact with the genetics of the host plant cultivars.
Disease management is addressed once the diagnosis of a plant disease has been made and the causal agent is identified. An analysis of the host and its symptoms, the identification of the fungal pathogen present, an understanding of how it caused the disease, and any environment factors that may have contributed to the development of the disease and spread of the fungus is determined. It is interesting to note that azole antifungal agents are used in human mycology, veterinary mycology, and plant pathology. They are used because the same groups of fungi cause disease in humans, animals and plants. The implications of this for development of resistance are unknown.
An interesting area of plant pathology is understanding at the molecular level how plant diseases develop. There is includes plant physiology, fungal physiology, biochemistry, and the genetics of the host-pathogen relationship. Areas of special interest are the specificity of the fungus-plant interaction, how the fungus recognizes the plant host, how the fungus gains entrance into the plant, the role of fungal toxins during disease development, how plant metabolism is modified, plant resistance mechanisms, and gene expression during host-pathogen interactions.
In the normal healthy indoor environment, isolated fungal species are usually similar to those of the outdoor air. Interpretation of indoor air sample results is based on a comparison of indoor and outdoor samples. In buildings that are tightly sealed, especially when air conditioners are used, the indoor air counts should be 30-80% lower than those outdoors, especially for fungi such as Alternaria. Increased counts of fungi suggests a problem with the Heating, Ventilation and Air Conditioning system.
There are no guidelines or regulations that can be used to indicate if the environment is safe or not. As an example, hospitals typically use, as air quality goals for their patient care areas, about 0.1 colony forming units (CFU)/m3 of Aspergillus and 1 CFU/m3 for other thermo-tolerant fungi.
There is a clear correlation between some fungi, health problems and moist-to-wet indoor environments that are caused by water damage. In such buildings, individuals frequently develop respiratory symptoms. One measure of the ability for a fungus to grow in a moist environment is its Aw, that is, its Water Activity (Equilibrium relative humidity/100) value. Fungi with high Aw values like to grow in wetter environments. For example, Stachybotrys chartarum is associated with wet areas has an optimum Aw value of 0.98 or greater. Penicillium and Cladosporium herbarium, both of which are associated with dryer areas, have Aw values of 0.78-0.88 and 0.88, respectively. In addition, a relative humidity greater than 55% and temperature fluctuations are ideal for mycotoxin production by Stachybotrys chartarum.
Aerosols caused by splashing of machinery in recycled cooling water which may build up a concentration of fungi, as well as bacteria, is the major concern for the work force in such workplaces.