Reduce your risk of exposure to swimmer's itch this summer
By: Les Riess, M.D.
Minnesota summers can be filled with a number of annoying pests. Mosquitoes and gnats buzz through the air. Poison ivy litters the forest floor. Ticks lie waiting in the trees or grass. Even the water of our 10,000 lakes has its share of parasites, not the least of which is the microscopic organism, schisosome cercariae, which causes the affliction known to most of us as “swimmer’s itch.”
Swimmer’s itch, technically called cercarial dermatitis, is a skin rash characterized by red itchy welts that appear on your skin within several hours after swimming in lake water that is infested with the schisosome cercariae parasite. It is a widespread occurrence throughout Minnesota and has been reported across the United States and as far away as Europe.
The parasite that causes swimmer’s itch has a complex life cycle. As adults, the parasitic flatworms live in the blood of lake mammals and birds, quite often ducks. The adult parasite sheds its eggs through the host’s excretory tract, where they most often land in the water. Here, the eggs hatch and enter a free-swimming stage where they search for a certain type of snail that serves as host for this part of their life cycle. The parasites spend three to four weeks within the snail before being released again into the water to enter the cercariae stage. The cercariae search for a host mammal or bird, but sometimes find a human instead. When cercariae mistake a human for a mammal or bird host, they burrows into the skin, causing the uncomfortable condition known as swimmer’s itch.
Even though the parasite tries to catch a ride on human skin, we can’t serve as hosts for the organism. Our body’s immune system recognizes the parasitic cercariae as foreign proteins and attacks and kills them shortly after they burrow into the skin. The severe itch and red welts are symptoms of an allergic reaction to the parasite. This rash remains from several days to two weeks, depending on your sensitivity.
Symptoms, which usually occur several hours after being in contact with contaminated water, can include tingling, burning, itching, red raised welts and small blisters on the skin. Scratching the affected areas can lead to bacterial infection and should be avoided. Over-the-counter treatments may help to decrease discomfort and itching. They include Calamine lotion, an antihistaminic or mild corticosteroid cream, applying cool compresses, bathing in Epson salts or colloidal oatmeal (Aveeno) and applying a baking soda paste to the rash.
If the rash and itching are so severe that you cannot keep from scratching, or if your rash becomes infected -- with pus, increased pain or redness -- contact your health care provider. He or she may suggest prescription-strength measures such as antihistamines and topical steroid creams to lessen your symptoms.
Swimmer’s itch is only one of a number of rashes that can occur after exposure to infected water, and there are a number of other skin conditions that might be confused with swimmer’s itch including impetigo, chickenpox, poison ivy and herpes. Your physician can help determine whether your rash is caused by swimmer’s itch or something else. Making a specific diagnosis is difficult, however, due in large part to the fact that there is no widely available medical test to confirm swimmer’s itch. The best confirmation is often based on the knowledge that others who have been in contact with the same lake also have the same rash.
Not everyone who comes into contact with the parasite will get swimmer’s itch. It’s estimated that between 30 to 40 percent of people coming into contact with the parasites will develop the rash. If you are allergic, it is likely that your rash will become more severe with each exposure.
No one wants to take swimmer’s itch home as a souvenir from the lake this summer, and there are a number of things you can do to prevent yourself from contracting this unpleasant rash.
Two of the most obvious are to stay away from marshy, weedy areas where snails are most commonly found and avoid sharing your swimming area with ducks or other aquatic birds such as geese.
While the cercariae parasite can enter your skin while you are swimming or wading, they often burrow into the skin when a person goes onto shore. Drying off thoroughly and rigorously after leaving the water destroys the parasites before they can enter the skin.
The cercariae stage that leads to swimmer’s itch lasts only about a day or so and the parasites tend to stay in the upper few inches of water. This tends to concentrate their numbers along the shoreline. Swimming in the lake, versus wading or sitting in the shallows, can help avoid contact.
Shower with soap and change into dry clothes as soon as possible after swimming.
Minnesota summers are short, and our lakes are some of our best and most beautiful resources. Don’t let swimmer’s itch keep you from enjoying the water this summer. Although the rash can be an annoyance and its symptoms can be frustrating, there are no permanent effects and most people recover gradually within a few days to a few weeks. Over-the-counter treatments are usually all that are needed to relieve the itching and pain associated with the rash, but your best bet is to try to avoid this summer nuisance by following steps to reduce your risk of exposure, such as drying off thoroughly with a towel each time you leave the water.
Dr. Riess is a board certified family practice physician at Raiter Clinic.