Swimmer’s Itch (Cercarial Dermatitis)

What is Swimmer's Itch?

Swimmer’s itch (also called cercarial dermatitis) appears as a rash on this skin. It caused by an allergic reaction to certain parasites that infect some birds and mammals. These microscopic parasites are released from infected snails into fresh and salt water (such as lakes, ponds and oceans). The parasite prefers certain birds or mammals (not humans). But if it comes into contact with a swimmer, it burrows into the skin and causes an allergic reaction and rash. Swimmer’s itch is more common during the warmer months, and is found around the world.

Swimmer’s itch is not the only rash that you may get after swimming in fresh or salt water.

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How do parasites get into the water?

The adult parasite lives in the blood of infected animals such as ducks, geese, gulls, swans, and some 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 water, they hatch and release small larvae. These larvae swim in search of a certain species of aquatic snail.

If the larvae find one of these snails, they infect the snail, multiply and develop further. Infected snails release a different type of larvae (or cercariae) into the water. This larval form then swims about searching for a suitable host (bird, muskrat) to continue its life cycle. Although humans are not suitable hosts, the larvae burrow into the swimmer’s skin, and may cause an allergic reaction and rash.

Because these larvae cannot develop inside a human, they soon die.

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What are the signs and symptoms of swimmer's itch?

Within minutes 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. Scratching the areas may result in secondary bacterial infections. Itching may last up to a week or more, but will gradually go away.

Swimmer’s itch is caused by an allergic reaction to infection, so the more 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.

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Should I see my health care provider for treatment?

Most cases of swimmer’s itch do not require medical attention. If you have a rash, you may try the following for relief:

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Can swimmer's itch be spread from person to person?

Swimmer’s itch is not contagious and cannot be spread from one person to another.

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Who is at risk for swimmer's itch?

Anyone who swims or wades in infested water may be at risk. Larvae are more likely to be in shallow water by the shoreline. Children are most often affected because they tend to swim, wade and play in the shallow water, and are less likely to towel dry themselves when leaving the water.

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Once water is contaminated, will it always be unsafe?

No. Many 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. But there is no way to know how long water may be unsafe.

Larvae generally survive 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.

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Is it safe to swim in my pool?

Yes. As long as your swimming pool is well maintained and chlorinated, there is no risk of swimmer’s itch. The specific type of snails must be present in order for swimmer’s itch to occur.

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What can be done to reduce the risk of swimmer's itch?

Towel dry or shower immediately after leaving the water.

Encourage health officials to post signs on shorelines where swimmer's itch is a current problem.

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For more information

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