As waters get warm, swimmers start itching

It's baaack.

As predictable as the swallows returning to Capistrano, swimmer's itch arrives from mid-July to early August in warm, shallow waters around the Flathead.

Boni Stout, director of community health at the Flathead City-County Health Department, confirmed that swimmer's itch, a rash caused by a parasite, has made its summer appearance.

"We have had some calls," she said.

The Health Department has decided not to publicize the locations where people have reported contracting swimmer's itch, Stout said.

"We want people to use universal precaution," she said.

Stout said swimmers should assume that any shallow, warm water may contain the parasite, called cercariae, and take appropriate precautions.

Health officials recommend that people swim off boats or docks in deeper, colder water to avoid the parasite.

"Obviously, that's not appropriate for young children," Stout said. "That's why they should towel off immediately."

If not wiped off with a towel, cercariae burrow into the skin of the swimmer. Although the parasites die, their presence causes an allergic reaction called cercarial dermatitis.

Health officials say the rash is not dangerous. However, it may itch intensely.

Stout said people who have had swimmer's itch may have a worse reaction the second time.

"The body becomes sensitized to it," she said.

Symptoms of swimmer's itch include a tingling, burning or itching within minutes to days of swimming in infected water. A small, reddish raised rash typically appears within 12 hours.

The rash may develop into small blisters. Itching may last a week or more but eventually disappears.

The Health Department recommends corticosteroid cream, cool compresses, bathing with baking soda, a paste of baking soda, an anti-itch lotion or colloidal oatmeal baths to relieve the itching.

In some cases, children may develop a secondary infection from scratching, which requires treatment from a health-care provider.

Stout couldn't predict how long the cercariae may inhabit the water. She said phone calls to the Health Department typically cease when children return to school and the swimming season ends.

The aquatic troublemaker has been traced to a parasitic flatworm called Trichobilharzia ocellata. University of Montana researcher Bill Granath Jr. studied the life cycle of the worm during the 1990s in Flathead Lake.

He found common merganser ducks and tiny snails were natural hosts. The parasite also occasionally penetrates seagulls and Canada geese but causes no harm to any of its hosts.

Because flatworms live in the blood of infected animals, they are often called blood flukes. After mating, the female flatworm's eggs exit the host in its feces.

Each egg hatches a larvae called miracidia, which has only a few hours to find a host snail. When in the snail, the miracidia reproduces, then becomes the itch-producing cercariae form of the parasite.

Described as a sperm-shaped creature with a forked tail, the cercariae exit directly out the flesh of the snail in search of a duck or other creature to penetrate and start the whole cycle over again.

If a swimmer picks up a cercariae and doesn't towel off, the evaporating water prompts the parasite to burrow into the skin.

According to Granath's research, the cercariae soon dies in human skin, releasing enzymes and waste products that cause inflammation and itching.

Granath recommended the same precautions as local health officials. In addition, he suggested wearing a coating of baby oil or waterproof sunscreen as a temporary barrier to the burrowing parasite.

People with questions about swimmer's itch should call the Flathead City-County Health Department at 751-8110.