Bird moving ban has some worried swimmers will be itching for relief

• A federal pause on waterfowl relocations because of the ongoing bird flu outbreak has prompted concerns over swimmer’s itch cases in northern Michigan lakes
• Mergansers, a key host for the parasite behind the rash, can no longer be moved, disrupting successful itch-reduction programs
• With bird-targeted strategies stalled, human-focused solutions to stop the parasite’s skin-burrowing larvae are back in focus

Duncan Lawrence saw the full ramifications of cercarial dermatitis — better known by its dreaded nickname “swimmer’s itch” — after his grandchildren experienced the allergic reaction firsthand at his cottage near Roscommon.

The three school-aged kids came out from playing in Higgins Lake and within hours were pockmarked with little red welts up and down their extremities. The grandfather remembers it being especially bad for one of the boys.
“I think it took him probably a week to recover,” Lawrence told Bridge Michigan.

Michigan is a hotbed for the rashy ailment — which shows up once out of every 15 times people swim in certain Up North lakes, according to one study — because of the state’s high number of recreational lakes where parasite-laden waterfowl flock near popular swimming spots. More than 30 lake associations are part of the Michigan Swimmer’s Itch Partnership formed to combat the problem.

But this year, a decision from the US Fish and Wildlife Service amid the multi-state outbreak of highly pathogenic avian influenza halted what many call the best deterrent against the condition — the relocation of common mergansers and their ducklings. The decision stops programs on four Michigan lakes — Larks, Douglas, Higgins and Crystal lakes — and prevents others from joining the effort. 

Dave Wynne, who handles swimmer’s itch issues for the Crystal Lake Watershed Association, believes the rash has pushed renters and tourists away from visiting the lake in Benzie County. He worries the ban on moving the birds will stop the progress his group has made.

“I think it's a broad-brush treatment for something that doesn't need to be stopped,” Wynne said. 

Bird flu has been detected in merganser populations across the Midwest. In February, hundreds of mergansers were found dead on the shores of Lake Michigan in Chicago in a suspected bird flu die-off.

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Wildlife die-offs from bird flu have been documented in Michigan since 2022. As of June 6, 33 wildlife samples in the state tested positive for bird flu this year, with 75 cases pending.

With relocation efforts paused indefinitely, lake association members and researchers have started to look at other options to stop mergansers from spreading parasites.

Some advocate for capturing the birds and giving them an anti-parsitic drug called praziquantel to stop parasitic eggs from developing and dropping in the water. Others call for culling or euthanizing mergansers to reduce their populations. 

So far, neither method has been approved by the Michigan Department of Natural Resources.

A rash decision

Lawrence likens swimmer’s 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’s itch,” Lawrence said.

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

“Every lake we've worked on has shown a huge decrease in the number of swimmer’s 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’s 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’s south region, which includes Frankfort, Manistee and Cadillac.

Swimmer’s 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 check to see which lakes are reporting cases of swimmer’s itch 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’s 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’s initial research in Michigan.

Blankespoor, the Jackson College professor, estimates “20 to 30 different species of parasite” cause swimmer’s 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’s 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’s 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.”