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Article title: Cercarial dermatitis: DPD
Conditions: Cercarial dermatitis
itch, also called cercarial dermatitis, is a skin rash caused by an allergic
reaction to infection with certain parasites of birds and mammals. These
microscopic parasites are released from infected snails to swim in fresh
and salt water, such as lakes, ponds, and oceans used for swimming and
wading. Infection is found throughout the world. Swimmer's itch generally
occurs during summer months.
to days after swimming in contaminated water, you may experience tingling,
burning, or itching of the skin. Small reddish pimples appear within 12
hours. Pimples may develop into small blisters. Itching may last up to
a week or more, but will gradually go away.
itch is caused by an allergic reaction to infection, the more often you
swim or wade in contaminated water, the more likely you are to develop
more serious symptoms. The greater the number of exposures to contaminated
water, the more intense and immediate symptoms of swimmer's itch will
Be aware that there are other causes of rash that may occur after swimming in fresh and salt water.
No. Most cases do not require medical attention.
If you have a rash, you may try the following for relief:
Try not to scratch. Scratching may cause the rash to become infected. If itching is severe, your health care provider may prescribe lotion or creams to lessen your symptoms.
The adult parasite lives in the blood of infected animals such as ducks, geese, gulls, swans, as well as certain aquatic mammals such as muskrats and beavers. The parasites produce eggs that are passed in the feces of infected birds or mammals.
If the eggs land in the water, the water becomes contaminated. Eggs hatch, releasing small, free-swimming larvae. These larvae swim in the water in search of a certain species of aquatic snail.
If the larvae find one of these snails, they infect the snail and undergo further development. Infected snails release a different type of larvae (cercariae, hence the name cercarial dermatitis) into the water. This larval form then searches for a suitable host (bird, muskrat) so they can start the lifecycle over again. Although humans are not a suitable host, the larvae burrow into the skin of swimmers, which may cause an allergic reaction/rash. The larvae cannot develop inside a human and they soon die.
Once an outbreak of swimmer's itch has occurred in water, will the water always be unsafe?
factors must be present for swimmer's itch to become a problem in water.
Since these factors change (sometimes within a swim season), swimmer's
itch will not always be a problem. However, there is no way to know how
long water may be unsafe. Larvae are generally infective for 24 hours
once they are released from the snail. However, an infected snail will
continue to produce cercariae throughout the remainder of its life. For
future snails to become infected, migratory birds or mammals in the area
must also be infected so the lifecycle can continue.
Yes. As long as your swimming pool is well-maintained and chlorinated, there is no risk of swimmer's itch.
This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care provider.
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