With summer comes another common nuisance, swimmer's itch. See the fact sheet below for more information.
WISCONSIN DIVISION OF PUBLIC HEALTH
Department of Health Services
"Swimmer's Itch"
(cercarial dermatitis, schistosome dermatitis)
Disease Fact Sheet Series
What is swimmer's itch?
Swimmer's itch is a skin rash caused by a parasite (shistosomes) which ordinarily infect birds, semi-
aquatic mammals, and snails. Common grackles, red-winged blackbirds, ducks, geese, swans,
muskrats and moles have been found to carry the parasite. As part of their developmental life cycle,
these parasites are released from infected snails, migrate through the water, and are capable of
penetrating the skin of man. After penetration, these parasites remain in the skin and die but can
cause an allergic reaction in some people. The parasite in man does not mature, reproduce or cause
any permanent infection.
Who gets swimmer's itch?
Only about one third of the people who come in contact with the parasite develop swimmer's itch.
People who swim or wade in infested water may experience this itchy rash. All age groups and both
sexes can be involved, but children are most often infected due to their habits of swimming or wading
in shallow water and playing on the beach as the water evaporates from the skin. Swimmer's itch may
be prevalent among bathers in lakes in many parts of the world, including the Great Lakes region of
North America and certain coastal beaches.
How is swimmer's itch spread?
An individual may get the infection by swimming or wading in infested water and then allowing water
to evaporate off the skin rather than drying the skin with a towel. Person-to-person spread does not
occur.
What are the symptoms of swimmer's itch?
Whenever infested water is allowed to evaporate off the skin, an initial tingling sensation may be felt
associated with the penetration of the parasite into the skin. The irritated spot reaches its maximum
size after about 24 hours; the itching may continue for several days. The symptoms should disappear
within a week.
How soon do the symptoms begin?
A person's first exposure to infested water may not result in the itchy rash. Repeated exposure
increases a person's allergic sensitivity to the parasite and increases the likelihood of rash
development. Symptoms may appear within 1 to 2 hours of exposure.
What is the treatment for swimmer's itch?
There is no treatment necessary for swimmer’s itch. Some people may get relief from the itching by
applying skin lotions or creams to the infected site.
When can you get swimmer's itch?
The first outbreaks usually occur in late May or early June. The outbreaks in Wisconsin may last from
2-weeks in the northern lakes to a month in the southern lakes. In some lakes it may last the entire
summer.
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What can be done to reduce the chances of getting swimmer's itch?
• Toweling off immediately after swimming or wading in infested water can be very helpful in
preventing rash development.
• Swim in water away from the shore.
• Avoid swimming in areas where snails have accumulated.
• Don't encourage birds to stay near swimming areas by feeding them.
DEVELOPED BY THE DIVISION OF PUBLIC HEALTH, BUREAU OF COMMUNICABLE DISEASE
COMMUNICABLE DISEASE EPIDEMIOLOGY SECTION
P-42094 (Rev. 05/04)
