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Website tracks outbreaks of swimmer's itch across North American lakes

A new website that allows the public to report cases and track outbreaks of swimmer's itch—cercarial dermatitis—across North America has been launched by the University of Alberta (U of A).

The site,, allows people report their own cases of the rash—caused by parasite larva burrowing into the skin—and alert other individuals to problem areas around the continent. The site also has information about the condition and the parasites, typically found in aquatic snails, that are its cause. Visitors to the site can also complete a survey that helps U of A researchers pinpoint when and where the parasites that cause swimmer’s itch are most prevalent.

“We want to help people make informed choices about where they swim by providing information on where swimmer’s itch is occurring and through education, which is what the website provides. We want to use it as a tool to connect with people,” said Patrick Hanington, PhD, in a press release from the university. Dr. Hanington is a researcher with U of A's school of public health.

The website generates a map based on reports from the public, flagging outbreaks—defined on the website as five or more swimmer’s itch reports received about the same lake in the same week—and factors such as wind and time of day that can influence where the parasites are most abundant so individuals can decide whether they want to visit a particular lake on a given day.

There does not appear to be any way to completely avoid risk of swimmer's itch when swimming in lakes. Dr. Hanington and his colleagues have studied self-reported survey data from 3,800 cases of swimmer's itch across Canada and the U.S. between 2013 and 2015, and they found that the rash could be a problem in any lake (Environmental Health Oct. 25, 2018;17:73). In Alberta alone, the self-report database has recorded case reports from 101 lakes across the province.

Risk of itch is not a question of pollution either, according to the release. Alberta's lakes are relatively shallow and have a high nutrient content, which encourages large snail populations. And Dr. Hanington's team has found that every common aquatic snail species in Alberta carries at least one species of parasite that causes swimmer’s itch. As well, what is likely the most prevalent snail species in central Alberta, Stagnicola elodes, was found in every lake the team surveyed and is also able to transmit the parasite that causes the condition, Hanington noted.

“Lakes in Alberta often support high biodiversity of animals we recognize and the parasites that infect them. It’s important to keep that ecological value in mind; lakes aren’t meant to be as pristine as swimming pools.”

This does not mean people should necessarily avoid lake swimming, he said, comparing the itch-causing parasites to horseflies and mosquitoes—just a natural hazard of enjoying the outdoors. And much like a mosquito bite, swimmer's itch is not something which usually requires a doctor's visit.

“The first stop should be to the drugstore for anti-itch cream, even for bad cases,” he said, adding the secondary bacterial infection that can occur from excessive scratching is far worse than the itch itself.

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