Lake Swimmer's Itch Caused by Parasites

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Swimmer's itch pegged to parasites
Sept, 2004

Lois Verbrugge takes her research personally. When she built a home with her husband on a northern Michigan lake, her scientist's curiosity was piqued by the irritation her skin developed every time she went swimming.

"I started to swim and itched intensely afterward," notes Verbrugge, a professor and senior distinguished research scientist at the University of Michigan Institute of Gerontology, Ann Arbor. "I'm a curious person and started asking questions about what was in the lake."

Verbrugge examined the incidence and risk factors of swimmer's itch, the lay term for cercarial dermatitis, caused by parasites in the water. "Exposure to shallow water and areas with onshore winds are key risks for swimmer's itch." The more days a person is in the lake, the higher his or her chance for having an episode of the painful skin irritation. Like poison ivy or oak, swimmer's itch is a reaction of the skin to an irritant. Larvae of the parasite burrow into the skin of swimmers, causing red, itchy bumps.

When Verbrugge began exploring the epidemiology of swimmer's itch, she found that most existing research looked at ducks and snails, because the parasite that causes the itch has a two-host life cycle, first involving snails, and later ducks. Verbrugge felt it was important to study human effects if it was to be taken seriously as a public health concern.

Time spent in water waist deep or shallower increases the likelihood of irritation, as does being in areas of the lake with onshore or receiving winds--winds that blow in toward shore. Onshore winds keep locally produced cercariae in place while bringing in cercariae produced in other areas, so they become more concentrated.

Verbrugge maintains it is up to individual swimmers to take precautions. Her defense is to wear a full Lycra wetsuit to keep the parasite out of her skin. She never wades through shallow water near shore, instead walking out to the end of a long dock to get into the lake. She also showers immediately after coming in from a swim, using a stiff brush to loosen any invaders that may have found their way through.

COPYRIGHT 2004 Society for the Advancement of Education
COPYRIGHT 2004 Gale Group
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