brochure has been produced to answer the more frequent enquiries
received by the Ministry of Environment, Lands and Parks (now
called Ministry of Water, Land and Air Protection) on swimmers'
itch and to provide you with general information on related
water management concerns.
What is Swimmers' Itch?
itch is a natural phenomenon that occurs in many water
bodies in British Columbia. It is a temporary skin irritation
caused by an invisible parasite found in lakes and ponds.
A life cycle
diagram of the parasite is helpful to show the origin of swimmers'
itch. The adult parasite lives in the blood of birds, but the
eggs of the parasite are passed out of the bird and develop into
larvae (cercaria) which seek out snails. As the larvae mature,
they pass again into the water to search out a bird to inhabit,
but sometimes select a human by mistake. Swimmers' itch is the
rash which develops when human antibodies destroy the parasites.
Where is Swimmers' Itch Most Likely to Occur?
itch usually occurs during the warm summer months (June - September)
which coincides with heaviest beach use.
The larval stages of the parasite concentrate near the water
surface where they can contact birds and mammals. Wind will
tend to bring the organisms into the shallows, often some
distance from the snail hosts in which they had lived. The
highest incidence of infection seems to be late in the day
after a period of incoming wind.
What are the Symptoms?
are unsuitable hosts for the swimmers' itch larvae, which die
soon after entering the skin. Our body reacts to the intrusion
in the following manner:
sensations: shortly after emerging from the water, bathers
will notice a tingling sensation on exposed parts of the body.
spots: red spots will develop where the organism has
penetrated hair follicles.
hours later, the tingling sensation will disappear, and the
red spots will enlarge and become itchy like an insect bite.
The degree of discomfort varies with the sensitivity of the
individual, the severity of the infestation and prior exposure.
The condition may persist for a few days.
What Precautions Can I Take?
can reduce the chances of contracting swimmers' itch by:
areas known to be infested: make enquiries and look for swimmers'
itch advisory signs. Avoid dense aquatic vegetation where snails
are likely to occur. Enter the water from a boat or wharf,
rather than wading in from the beach, to limit exposure.
down: towelling down briskly upon leaving the water
may remove the parasite before it penetrates the skin.
a shower taken immediately after leaving the water may reduce
waterproof suntan lotion: some believe that use of a waterproof
suntan lotion may reduce the risk of infection.
What Can I Do if a Rash Develops?
physician can recommend the best treatment. Commonly prescribed
anti-itch lotion (e.g., Calamine Lotion)
a soda bath (three tablespoons in a shallow bath)
Is the Rash Dangerous?
allergic reaction to swimmers' itch can be unpleasant, but
the organism does not enter the blood and the rash does not
spread from the initial points of contact. Symptoms usually
last for four to five days, although they may persist for up
to two weeks.
Can Swimmers' Itch be Controlled at the Source?
was commonly believed that chemical treatment of snail populations
would break the life cycle of the parasite. However, such actions
can result in ecological damage and generally are not permitted
in public waters. Moreover, the floating stage of the swimmers'
itch organism may be blown or carried many hundreds of meters,
perhaps kilometers, from the snail source, making chemical
control of limited value.
Should I Report Swimmer's Itch?
the outbreak of cases appears to be severe, please notify the
nearest Ministry of Health office or other local authorities
(e.g. BC Parks if within a provincial park). The local authorities
may decide to post a warning to beach users.
Originally published in August 1998
updated: August 3, 2001