By John C. Wolf, D.O.
Associate Professor of Family Medicine
Ohio University College of Osteopathic Medicine

WATERBORNE PARASITE ON HUMAN SKIN EQUALS "SWIMMER'S ITCH"

Question: I spend a lot of time in the water during the summertime. I often swim in the lake that is close to my home, and I water-ski on most weekends. Last year I got a rash that itched rather severely. My doctor said it was swimmer's itch and that it would go away on its own. What causes swimmer's itch, and why did I get this last year when I haven't gotten it before?

Answer: Swimming, like most activities -- including getting out of bed in the morning -- has risk associated with it. An annoying one that is occasionally associated with swimming in lakes, ponds and rivers is a skin inflammation called "swimmer's itch." There are actually several conditions that go by that general name, but being in northern latitudes makes it likely your condition is caused by an allergic reaction to a parasite that causes illness in birds.

Swimmer's itch is a great example of the complexity of life. Let me start my explanation with the connection to waterfowl -- principally ducks, geese, gulls and swans. When these birds become infected with a parasite called a blood fluke, it produces eggs in the infected bird's digestive system. These eggs are then subsequently deposited along with the rest of the bird's "droppings."

Fluke eggs must be in water to hatch, and that condition is likely to occur considering the habitat of the host waterfowl. When the eggs hatch they produce free-swimming larvae called miracidia. These creatures can't infect waterfowl or humans. Instead, they must find an intermediate host -- a water snail -- to continue their life cycle. Once a snail becomes infected, the miracidia continues its development into a more evolved type of larvae called cercariae. These cercariae are then released into the water.

Cercariae aren't the most sophisticated creatures on our planet. They swim about until they find skin -- any skin -- to burrow into. If the skin belongs to a waterfowl, then the life cycle continues with development into another blood fluke. When a cercarium burrows into human skin, no further development occurs. The creature dies within the skin. It is a reaction to dead cercariae that causes swimmer's itch -- what we doctors also refer to as cercarial dermatitis.

Swimmer's itch begins minutes to hours after swimming in infected water. A tingling, burning or itching feeling starts first. Then, red pimples appear in the itching areas. These pimples can then progress into blisters that typically go away in about one week.

Treatments that help most itching skin rashes work for swimmer's itch, too. Cool compresses, baking soda baths, hydrocortisone cream or Calamine lotion all help relieve the symptoms.
Fortunately, you can't give swimmer's itch to someone else. However, other people who swim where you encountered the cercariae are at risk for getting it. Therefore you should stay away from that "swimming hole" for the rest of the season.

Because the life cycle of the blood fluke is complex, there is a good chance that the lake, pond or river where you got swimmer's itch last year will be free of it this season as it was in the years before last summer. For some measure of security you could check with the local office of the State Department of Health to see if they have any reported cases of swimmer's itch this year. If they have, go swim in a swimming pool instead. Pools are immune from this particular problem because of the chlorine used to disinfect the pool water. If the pool has a lifeguard and your "swimming hole" doesn't, you are also much less likely to drown in the pool. That's another important safety consideration!

"Family Medicine" is a weekly column. To submit questions, write to John C. Wolf, D.O., Ohio University College of Osteopathic Medicine, P.O. Box 110, Athens, Ohio 45701. Past columns are available online at http://www.FamilyMedicineNews.org.