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A rash decision

Lawrence likens swimmer itch to an aquatic version of a bad poison ivy reaction.

For a moment, the cherished childhood memories the 67-year-old thought he could offer the next generation of his family were thrown into uncertainty.

“They were choosing not to spend time up here in part because of the swimmer itch,” Lawrence said.

The experience pushed Lawrence toward a volunteer position on the Higgins Lake Property Owners Association, where he now heads the group swimmer’s itch organization.

As chair, Lawrence leads the effort to mitigate and research the condition for the more than 1,000 property owners on the lake, hosting annual fundraising events to fund the efforts. He estimates they spend about $20,000 a year on the problem.

The Michigan Swimmer Itch Partnership formed in 2014. The group pooled together resources and exchanged information, leading a successful campaign to allocate $750,000 in one-time state funding to stop swimmer itch.

The result has been a boon for researchers and swimmers, with lakes reporting significant reductions in cases.

One of the leading strategies the funding supported was merganser brood relocation

Canadian geese and mallards have both been identified as parasite-hosting species, but the common merganser is seen as the leading avian host for the species of parasite most commonly found to cause swimmer itch in Michigan.

“Every lake we’ve worked on has shown a huge decrease in the number of swimmer itch cases,” said Curtis Blankespoor, a Jackson College biology professor whose family has led efforts to remove mergansers from lakes to great effect.

In past years, associations on Larks, Douglas, Higgins and Crystal lakes have adopted trap and relocate procedures for mergansers in coordination with the DNR.

While the DNR suspended the program 2022 and 2023 during the onset of the bird flu outbreak, a spokesman for the agency confirmed the federal government intervened this year to stop the duck relocation.

Patrick Hanington, who studies how parasites infect humans at the University of Alberta, said there not a “one size fits all solution” to swimmer’s itch.

Some lakes with reports of the rash have different types of parasites and merganser relocation would be less effective there. The effect of removing one of the top predatory birds from the lake ecosystem would “certainly have consequences for the fish communities.

“It’s not a silver bullet for solving swimmer’s itch,” Hanington said. “These parasites … they’re not problems from an ecological perspective. They actually serve as an important food source for filter-feeding organisms.”

Time stops the itch

Once it materializes, not much will stop the rash from running its course. The parasites will eventually die under the skin.

“The treatment is really time,” said Dr. Brian McComb, chief medical officer for Muson Healthcare south region, which includes Frankfort, Manistee and Cadillac.

Swimmer itch is generally “short-lived,” according to McComb, with superficial bacterial infections from scratching being the biggest risk associated with the rash. Most treatment is focused on symptom relief.

“Sometimes, cold compresses will help,” he said. “Sometimes, hydrocortisone or steroid cream will help. Antihistamines often help. You can use baking soda paste to help with the itching, as well.”

McComb advises people to  to decrease their chances of getting the rash.

With strategies targeting birds momentarily out of reach, human-centered solutions that stop the parasite from entering the skin are still on the table.

Wet suits, rash guards and petroleum jelly can act as barriers to stop the larvae from reaching the skin. Swim baffle systems and parasite skimmers create areas on the lake with fewer microorganisms. Adjusting swim times to the afternoon or swimming with offshore wind can also reduce infection.

The complex life of avian schistosomes

When William Walter Cort of Johns Hopkins University arrived on Douglas Lake in 1914, nobody knew what was causing the rashes afflicting both the University of Michigan Biological Station researchers who waded into the waters to gather specimens and the sunbathing summer resort swimmers nearby.

It was during his return visit as faculty a decade later that Cort, who’d be remembered as a “master hookworm investigator,” successfully isolated a larval parasitic flatworm, placed it on human skin and yielded the same itchy skin condition the U-M biologists had been observing for years.

Cort 1928 publication in the Journal of the American Medical Association was the first to link the complex life cycle of parasitic flatworms known as avian schistosomes to what was then referred to as “water itch.”

Since then, parasitologists have worked to refine Cort initial research in Michigan.

Blankespoor, the Jackson College professor, estimates “20 to 30 different species of parasite” cause swimmer itch — their reproduction contingent on infecting other organisms.

Schistosoma eggs enter the water through feces from animals such as geese and ducks. Once there, they hatch larvae called miracidia, which float around until one finds a snail to penetrate.

Within the snail, the parasite reproduces asexually, multiplying until the snail releases secondary larvae called cercariae —  microscopic, tadpole-like things that swim toward surface waters, where they wait to enter their next host.

“A single snail that’s infected with one of these parasites will release potentially thousands of the next life cycle stage into the water on a daily basis after it’s been infected for about a month,” said Hanington, the University of Alberta researcher.

The parasitic larva reproduction cycle culminates when it infects the birds that thrive in freshwater lakes and rivers. The cercariae burrow into their bodies, enter blood vessels, mature into adult worms and lay eggs to begin the cycle anew.

When the parasitic larvae mistakenly find the wrong host in humans, swimmer itch arises.

Unable to fully penetrate our bodies, the cercariae embed themselves in the skin, causing an allergic irritation that looks like blisters or pimples at each infection site. Cercarial dermatitis gets its name from the cercariae.

It just so happens that lake-loving humans often occupy spaces that cercariae also share.

“They tend to come out from the snails in sort of the most abundance early in the morning,” Hanington said. “They tend to be up at the top of the water column. But, because of the wind and wave action, they tend to be closer to the shoreline.”

The life cycle of cercarial dermatitis. Photo courtesy of the US Centers for Disease Control and Prevention.

The Common merganser, a large fish-eating duck that thrives in large lakes and rivers in northern forested habitats. Photo courtesy of Tom Koerner/US Fish and Wildlife Service.

Swimmer itch as it appears on a leg (left) in comparison with a leg treated with a proprietary swimmer itch repellant (right). Photo courtesy of Wayne Swallow.

A couple cleans their inflatable after swimming in Higgins Lake. Photo credit: Josh Boland / Bridge Michigan.