Battling Swimmer’s Itch…and Winning

Posted on September 24, 2008 by glenlake

Common Mergansers

Summer traditions returned this past season on Glen Lake and some were more popular than others. Cottage owners, year-round residents and visitors to the Glens maximized their enjoyment of the 2008 season with typical outdoor activities. There were plenty of cook-outs, water-skiing, sailing, fishing forays and resulting fables, beach parties and … swimmer’s itch.

As long as most can remember, this pesky nuisance has been associated with some susceptible swimmers, and not just on Glen Lake, but throughout the north’s inland waterways and the northern tier of states. Locally, the situation has improved thanks to the efforts of the Glen Lake Association and experts they are working with.

“Although we are unable to totally eliminate swimmer’s itch here or anywhere else, GLA has made significant improvement with fewer swimmer’s itch cases reported each year,” explains Rob Karner, Glen Lake/Crystal River Watershed Biologist. “It’s a natural occurrence that most people don’t contract. However, 30 percent of the population is susceptible if exposed.”

The annoying, itchy, red bumps known as schistosomal dermatitis, is a short-term, immune reaction occurring in the skin of humans that have been infected by water-borne parasites. Symptoms, which include itchy, raised papules, commonly occur within hours of infection and do not generally last more than a few days.

With the assistance of Dr. Harvey Blankespoor, the leading parasitologist in the Midwest, who has worked closely with the Glen Lake Association over the past three decades, have pinpointed the two hosts which complete the life cycle in Glen Lake. And by the way, each lake in northern Michigan may have their unique hosts that may differ from Glen Lake. In our lake, the two hosts are Stagnicola snails, and the Common Merganser duck.

In order to rid a lake of swimmer’s itch, researchers and their teams work to break the cycle of parasitic flatworms called schistosomes, that live part of their life cycle in snails and part in birds. According to Dr. Blankespoor’s findings, schistosome eggs from infected fecal matter from waterfowl are deposited in the lake. The eggs, known as miracidia, hatch and find a host snail to infect. It is during the next few weeks of the cycle that humans are vulnerable. Schistomsome larvae, called cercarium, migrate from the snail and swim around looking for another host, usually a bird. Incapable of being seen by the naked eye, this tiny organism propels itself through the water and bores into the skin to reach a host’s bloodstream. At that point the life cycle begins again with parasite eggs released in water fowl fecal material. If the cercarium accidentally penetrate the skin of a sensitive human, the parasites are unable to pass through the epidermis. They soon die, causing an allergic reaction ending with the formation of a papule (i.e., a red, raised itchy spot).

In the 1980’s and many years prior, copper sulfate was used to eliminate the nine species of snails found in Glen Lake. Karner said the applications were not only expensive, but eliminated all the snails, which he calls “the lawn mowers on the lake bottom,” keeping algae growth under control. Plus, the long term affect of this chemical on the health of the lake is unknown.

For the past seven years, Karner and SiCon, Inc. (SiCon is an acronym for Swimmers Itch Control) have used a trap and relocate program to remove live mergansers from Glen Lake. Female mergansers and their broods are trapped, inoculated and relocated to Lake Michigan. Karner said the program is definitely working as each year there are fewer returning ducks, reduction in snail infection rates, and fewer cases of reported of swimmer’s itch. The association has sent over a thousand live snails to the University of Michigan lab for testing to monitor the effectiveness of the program.

“We have successfully reduced the parasite load in snails and without our merganser relocation program, swimmer’s itch would definitely increase,” said Karner. The cost of the program is about $7,500 a year compared to the $40,000 per year to chemically treat the lake using crop dusting airplanes. “It has been a huge improvement and a smarter plan. But even so, there are still those who think it is not working. Unfortunately, we cannot put a dome over Glen Lake when migrant ducks visit the lake each spring and fall, which could be part of the problem.”

Some, including Karner, believe the ultimate solution to the end of swimmer’s itch is an effective cream for topical use by humans.

However, that remedy has yet to be developed.

So what can you do to help? Please visit www.swimmersitch.org, and report any and all cases of swimmers itch online throughout the swimming season. Also, please do not harass Common Mergansers during June and July when we are trying to trap the ducks. Finally, consider buying into a “hot spot” treatment of your shore which physically removes only the target snail from your shoal by contacting Rob Karner at 231/334-5831.