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Swimmer's Itch

Swimmer's itch (also known as cercarial dermatitis) is a skin rash caused by an allergic reaction to microscopic parasites found in some waterfowl and aquatic mammals. Symptoms include itching, burning skin and small blisters. Medical attention is not usually required, and it can often be treated with a baking soda paste or by bathing in colloidal oatmeal.

What Is Swimmer's Itch?

Swimmer's itch, also called cercarial dermatitis, is a skin rash that is caused by an allergic reaction to certain parasites found in some birds and mammals. These microscopic parasites are released from infected snails into fresh and salt water (such as lakes, ponds, and oceans). Rather than finding a host bird or mammal, the parasite will burrow into a person's skin, causing an allergic reaction and rash.
 

Where Does Swimmer's Itch Occur?

Swimmer's itch occurs worldwide in every continent except Antarctica. In the United States, cases are commonly reported from the Great Lakes region.
 

How Does Water Become Infected?

The adult parasite lives in the blood of infected birds, such as ducks, geese, gulls, swans, and certain aquatic mammals, such as muskrats and beavers. The lifecycle of the parasite entails the following:
 
  • The parasites produce eggs that are passed in the feces of infected birds or mammals 
  • If the eggs land in the water, the water will become contaminated
  • Eggs hatch, releasing small, free-swimming larvae
  • The 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 called cercariae into the water
  • This larval form then swims about, searching for a suitable host (bird, muskrat) so they can start the lifecycle over again.
 
Although humans are not suitable hosts, the larvae can burrow into the swimmer's skin, and may cause an allergic reaction and rash. However, these larvae cannot develop inside a human, and therefore, they will soon die.
 
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