Swimmer’s itch: what is it?

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Swimmer’s itch is a skin condition caused by fluke parasites found in lakes and other slow-moving or shallow coastal bodies of water. It presents as raised, inflamed papules that typically go away on their own within a week. Prevention methods include using insect repellent and anthelmintics.

Swimmer’s itch, or cercarial dermatitis, is a skin condition caused by fluke parasites. The condition gets its nickname from the fact that the parasites are waterborne, making those who swim in lakes more susceptible. Other common names include duck itch and clam digger’s itch. Swimmer’s itch can be annoying, but it’s not a serious condition and typically goes away on its own within a week.

A variety of parasites can cause swimmer’s itch, although most are of the genus Trichobilharzia or Gigantobilharzia. Parasites usually infect birds or snails and accidentally attach themselves to humans. Flukes cannot survive in humans or other mammals and die within hours.

Swimmer’s itch presents as raised, inflamed papules that appear within hours of infection. The inflammation and itching are due to an immune reaction, similar to that which accompanies insect bites. Any raised area on infected skin is the site of a parasite penetration.

Swimming in lakes and other slow-moving or shallow coastal bodies of water puts you at risk for swimmer’s itch. The infection has been reported worldwide, from the United States to Europe to Southeast Asia. Swimmer’s itch can be prevented with the use of insect repellent DEET or the anthelmintic (parasitic worm killer) niclosamide, applied topically. In case of infection, topical and oral antihistamines are helpful against itching and no further treatment is needed.

Attempts to reduce the risk of swimmer’s itch focus primarily on mollusc or avian vectors of the parasite, either by reducing the population or by administering anthelmintics to chicks. However, the wider environmental effects of such methods are not well known.

Although swimmer’s itch isn’t a serious condition, the symptoms are similar to many other skin conditions of varying severity, so it’s important to monitor the rash in a suspected case of cercarial dermatitis. If symptoms do not improve within three days, see a dermatologist. Diseases such as chicken pox, herpes and impetigo have similar symptoms to swimmer’s itch in the early stages.

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