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Swimmer's itch, or cercarial dermatitis, is a skin condition caused by trematode parasites. The condition gets its nickname from the fact that the parasites are water-borne, making those who swim in lakes most susceptible. Other common names include duck itch and clam digger's itch. Swimmer's itch can be uncomfortable, but it is not a serious condition, and it typically goes away on its own within a week.
A variety of parasites can cause swimmer's itch, though most are of the Trichobilharzia or Gigantobilharzia genus. The parasites usually infect birds or snails and attach themselves to humans accidentally. The trematodes cannot survive in humans or other mammals and die within hours.
Swimmer's itch presents as raised, inflamed papules that appear within a few hours of infection. The inflammation and itch is due to an immune reaction, similar to that accompanying bug bites. Each raised area on infected skin is the site of a parasite penetration.
Swimming in lakes and other slow-moving or shallow inshore bodies of water puts one at risk for swimmer's itch. The infection has been reported around the world, from the United States to Europe to Southeast Asia. Swimmer's itch may be prevented by the use of the insect repellent DEET or the anthelmintic (parasitic worm killer) niclosamide, applied topically. In the case of infection, topical and oral antihistamines are helpful against itching, and no further treatment is necessary.
Attempts to lower the risk of swimmer's itch mostly focus on the mollusk or avian vectors of the parasite, either by reducing the population or by administering anthelmintics to infant fowl. However, the wider environmental effects of such methods are not well known.
While swimmer's itch is not a serious condition, the symptoms are similar to those of many other skin conditions of varying severity, so it is important to monitor the rash in a suspected case of cercarial dermatitis. If symptoms do not improve within three days, consult a dermatologist. Diseases such as chickenpox, herpes, and impetigo have similar symptoms to swimmer's itch in their early stages.