Disease Fact Sheet (Cercarial Dermatitis, Schistosome Dermatitis)
What is swimmer’s itch?
Swimmer’s itch is an itching, macular or papular skin rash caused by larval schistosomes
(trematode worms) called cercariae, which are parasites of shore birds, water fowl,
semi-aquatic mammals and snails, but not humans, in different stages of their life cycle.
Common grackles, red-winged blackbirds, ducks, geese, swans, muskrats and moles
have been found to carry these parasites. As part of their life cycle, these parasites are
released from infected snails, travel through the water and penetrate the skin of their
hosts. They will penetrate the skin of humans but die without completing their life cycle,
often causing an allergic skin reaction. The parasite does not mature, reproduce or
cause any permanent infection in humans. Other schistosome species can cause liver,
intestinal or urinary disorders.
Who gets swimmer’s itch?
About one third of the people coming into contact with the cercariae develop swimmer’s
itch. People who swim or wade in infested water may experience this itching rash. All
age groups and both sexes may be involved, but children are most often infected due to
How is swimmer’s itch spread?
Any individual can get the infection by swimming or wading in infested water and
allowing the water to evaporate off the skin rather than promptly drying with a towel.
Person-to-person transmission does not occur.
What are the symptoms of swimmer’s itch?
When infested water is allowed to evaporate off the skin, an initial tingling sensation
may be felt, which is associated with the penetration of the cercariae into the skin. The
irritated spots become macules or papules in 1-2 days, although itching may continue
for several days. The symptoms usually disappear within a week.
How soon do symptoms occur?
A tingling sensation may occur immediately after swimming or wading. The macular
rash appears within 1-2 hours of exposure. 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 cercariae and increases the likelihood of rash development.
What is the treatment for swimmer’s itch?
While all cases do not require treatment, some people may seek relief by applying
soothing skin lotions or creams to minimize the itching.
What can be done to prevent the spread of swimmer’s itch?
The outbreaks of swimmer’s itch usually begin in late May or early June. In some lakes
and ocean areas, infestation lasts the entire summer. Reducing the number of water
fowl and snails in swimming areas will greatly reduce the risk of swimmer’s itch infection
in those areas.
ODH-IDCM SWIMMER’S ITCH-1/Section-6 Revised 1/2009
What can be done to reduce the risk of getting swimmer’s itch?
• Towel off immediately after swimming or wading, especially children.
• Swim in water away from the shore.
• Avoid swimming immediately after an onshore wind if the lake is having a problem
with swimmer’s itch.
• Avoid swimming or wading in areas where snails have accumulated.
• Do not encourage birds to stay near swimming areas by feeding them.
ODH-IDCM SWIMMER’S ITCH-2/Section-6 Revised 1/2009
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