2018-07-26 / Life in Leelanau

Bye, Bye SWIMMERS ITCH

Lake groups join to fight a parasite


MERGANSER DUCKS scoot along the shoreline of Glen Lake. The waterfowl is a host for the parasite that causes Swimmer’s Itch, and efforts are ongoing to trap and move them to Suttons Bay. MERGANSER DUCKS scoot along the shoreline of Glen Lake. The waterfowl is a host for the parasite that causes Swimmer’s Itch, and efforts are ongoing to trap and move them to Suttons Bay. Approximately 100 merganser ducks are swimming in new waters, which should be a comforting thought for swimmers splashing around Leelanau County’s inland lakes.

Waterfowl are key in the lifecycle of the parasite that causes Swimmer’s Itch, something that hasn’t gone unnoticed by the Glen Lake Association, Lake Leelanau Lake Association, Lime Lake Association, the Michigan Swimmer’s Itch Partnership (MSIP), and Freshwater Solutions.

All of those groups have been working since 2016 to combat Swimmer’s Itch. And they’ve had some success as over 350 merganser ducks have been trapped and relocated since the inception of the program.

According to Glen Lake Association watershed biologist and MSIP scientific review committee chair Rob Karner, 99 merganser ducks were trapped on Glen Lake last year. Karner is hoping to relocate about the same number this year.


MERGANSERS CAUGHT and trapped are relocated to Suttons Bay where the environment does not support the development of the parasite that causes Swimmer’s Itch. MERGANSERS CAUGHT and trapped are relocated to Suttons Bay where the environment does not support the development of the parasite that causes Swimmer’s Itch. Lake Leelanau mergansers have been moved as well.

“To date, two hens have been tagged with geolocators and teams have removed four broods of chicks. The latest capture occurred Monday of a mother bird with 12 chicks. The broods have been relocated to a state-approved location in Suttons Bay,” said Wayne Swallow, Watershed Biologist for Lake Leelanau.

The hope is that forced migration to Suttons Bay, whose waters don’t support the life-cycle of the parasite, will reduce the overall number of incidents of Swimmer’s Itch.

It can be an expensive proposition by moving ducks one at a time. But the State of Michigan is helping to fund the effort with a $250,000 grant.

What is Swimmer’s Itch?

“The itch” in Swimmer’s Itch is not the result of a bite or a sting. It’s actually a reaction to a parasitic worm that’s looking for an avian host — a merganser, to be specific. According to the MSIP website, the worm, or larval stage of a parasitic flatworm, hatches from eggs that end up in the feces of the bird.

If the feces lands in the water, the eggs hatch and larvae search for a snail to infect. On the journey, the worm may instead burrow under the skin of a human and die.

An itchy reaction in many people.

So the more birds that are removed, the less opportunity the parasite has for completing its life-cycle, Karner explained.

“It’s hard work,” Karner said. “What we took out two years ago lowered the counts of ‘worms in the water’ last year, what we took out last year lowers the counts for this year. We are hoping worm counts are low this year.”

“This method (of relocation) is shown to be effective,” Swallow said. “This process takes it down to negligible levels. After that, it’s just monitoring.”

While the technique seems to be working in some places, it’s not in others — such as the south end of Lake Leelanau, where Swallow says no mergansers have been found.

But there are more than one species of the itch-causing parasite. And each parasite has its own life cycle.

“We are trying to determine what birds and what snails are causing the Swimmer’s Itch,” Swallow said. “We have had quite a few cases… We think it might be the mallard and Canada geese, but we aren’t quite sure.

Karner said Glen Lake struggled with Swimmer’s Itch generated by mallard ducks in the past, but found a different solution.

“We have a lot of mallards around (on Glen Lake), but even if there’s a second worm working in the mallard, we basically use a deworming medicine which keeps the worms out of the (mallard) duck,” he said.

It’s a control measure that could be used on Lake Leelanau, Karner added — with more funding.

New Technology

Identification of the host waterfowl population could become easier thanks to a new water testing method.

The old method — which is still in use — requires a snail sample.

“You pick them up out of the water and put them in cups at daybreak, early in the morning — that’s when the snails are out — and look for worms to see if the snails are infected,” Swallow said.

Enter something called qPCR, (Quantitative polymerase chain reaction).

“I’m most excited about being able to use a new water test to differentiate between the three worms that cause Swimmer’s Itch in Leelanau County lakes,” Karner said. “This is brand new. The water tests the difference in these three species’ DNA. Once we find the unique genes in the one worm that’s different from the other two, this water test is really going to help us. It’s a lot less labor-intensive as well.”

For instance, if a sample indicates an 80 percent merganser influence and a 20 percent mallard influence, then Canada geese are ruled out. So pinpointing the avian host will be relatively simple.

Treatment possibilities

Regardless, Swimmer’s Itch is here to stay, Karner concedes.

“We are still going to have Swimmer’s Itch,” he said. “(Relocation) is not something that eradicates it — like smallpox or polio with a vaccine — but it will help.”

Other treatments include removing snails from an area by skimming the water’s surface. According to Karner, a special net catches worms on their search. Once caught, they are destroyed.

Regardless of how swimmer’s itch is fought in the future, the fight has to be better for the environment than past efforts.

At one time copper sulfate was spread in large quantities as a molluscicide. Karner said this method has not been used in several years because it was proved ineffective.

And obviously applying a metal to a lake bottom is bad for the environment.

Perhaps some day preventing Swimmer’s Itch will be as simple as avoiding a sunburn.

A wearable cream is available now to prevent the parasite from embedding in the skin. Swallow has been working for several years to develop his own.

“It’s going quite well,” he said. “I have finally isolated a couple of compounds that seem to do the trick.”

He’s the sole test subject so far, and the cream has proven effective 96 percent of the time.

Swimmers, try these precautions

The Michigan Swimmer’s Itch Partnership website, which is partially funded by the Glen Lake Assocation, offers these tips to avoid painful rashes:

 Don’t swim for long periods of time in shallow water;

 Avoid swimming in areas where Swimmer’s Itch is a known problem and where there is an onshore wind;

 For riparians, do not encourage birds to stay in your area;

 Avoid placing rip-rap on your shoreline. It provides a surface for certain species of snails to attach their eggs. And with more snails comes a greater chance for Swimmer’s Itch;

 Vigorously towel off after swimming.

Return to top