An Historical Look at Swimmer’s Itch

An Historical Look at Swimmer’s Itch

History of Swimmer’s Itch:
The presence of SI has been recorded as far back as the early logging days. Data on SI has been collected since 1929 by the Michigan Department of Natural Resources (then DNR and now EGLE). The quantity of copper sulfate applied in individual lakes has been recorded since 1947.

Glen Lake Association: In 1945 when the GLA was formed SI was one of the first issues that required their attention. Property owners were complaining and businesses were concerned about the potential negative effects that high levels of SI could have to the summer economy. The history of GLA strategies for addressing SI can be divided into five phases: 1. Application of Copper Sulfate (1947-1981) on a lake wide basis. Application continued through 2000 in small targeted areas. 2. Trapping and relocating the common merganser hens and their broods, Mid 80’s-2009 and again in 2017-2019. 3. Harassment 2010-2015 4. DNA Testing 2017-Present 5. Prevention 2020.

Phase I: Copper Sulfate Copper Sulfate was first applied in 1947 and ended in 1981 on a lake-wide basis. Applications continued on and off in small targeted area’s until 2000. Copper Sulfate was the only option the GLA had for nearly four decades to control SI. The purpose of the copper sulfate was to kill the snail that was a key component in the life cycle of the parasite that causes SI. Properties of Copper Sulfate are: 1. Heavy metal 2. Accumulates in the lake sediment and in the living tissues of aquatic animals. 3. Can pose a significant threat to the aquatic environment. 4. Is a nonspecific poison. Effectiveness of Copper Sulfate: 1. Not effective below six feet. 2. Dilutes quickly and is only effective for approximately two hours. 3. Accumulates on the bottom and kills the snails, but also other unintended aquatic life. 4. The parasites drift with the currents and winds moving into untreated areas. 5. Snails are mobile and can move into treated areas within a few weeks, replacing the dead snails.

While collecting this information on SI, I spent several hours interviewing Rob Karner. He has a wealth of information and is most helpful. He was hired on as the GLA’s resident biologist in 1980 and has never stopped looking for ways to preserve the water quality of Glen Lake and discover new ways of dealing with SI through research. I asked Rob what he thought about the effectiveness of copper sulfate and he gave it a moderate to low grade. The GLA focused on copper sulfate as the standard practice for controlling SI through the 40’s, 50’s, 60’s and 70’s. 1981: The GLA used twice as much copper sulfate as it had in 1980. There was no significant change in the number of cases of SI. 1982: The GLA sent a survey to its members asking if they should continue applying copper sulfate. The survey was split so the GLA board decided not to treat Glen Lake in 1982.

Phase II: 1983: The GLA was not getting the results they wanted from copper sulfate. They sent correspondence to MSU Cooperative Extension Service, Lt. Governor Connie Binsfeld and Michigan Department of Commerce looking for a grant. They received a $200,000 award from Michigan Department of Commerce to conduct a three-year study on SI. This groundbreaking study was in full swing in 1984 and completed in 1985. The study showed that 90% of SI came from a parasitic relationship between the common merganser and a specific snail. This understanding was revolutionary and lead to other ideas about possibilities for controlling Swimmer’s Itch. The thinking was that if the mergansers were removed from the lakes the life cycle of this parasite would be broken. In the mid 80’s the trapping and relocation of the female merganser and her brood began. The mergansers would be tagged, dewormed, and released. Over one 3-year period the percent rate of infection in snails went from 2% to 0.1%. GLA believed they had found the silver bullet. Mid 90’s-2004:  There was only sporadic trapping on the lake. 2004-2009:  GLA hired a company holding a research permit to trap and relocate the female mergansers and her brood. A reduction in the number of merganser hens and chicks was realized on the lake.

Phase III: 2010-2015: No trapping permits were issued by the DEQ and the GLA resorted to a new phase which they called harassment. This involved pursuing the mating pairs of mergansers in the spring with a power boat and shooting pyrotechnics in the hopes of discouraging mating and driving them from the lake. Harassment did not work. The ducks never left the lake and at the end of the sixth season there were more females and broods on the lake than ever. 2016: GLA did nothing.

Phase IV: DNA testing: 2017-2019: GLA received funding from the State of Michigan Commerce Dept. and a trapping and relocation permit from the DEQ. In addition, GLA began participation in a multiyear study using qPCR (Quantitative Polymerase Chain Reaction) technology to test for SI parasite DNA in water, snails, and birds. Much was learned, including the discovery that multiple species of SI parasite are affecting Glen Lake swimmers including a never discovered species! Also that Canada Geese and Mallard Ducks are contributing to SI life cycles. This helps explain why despite very successful trapping numbers over these three years, GLA saw an increase in the number of each cases each year. Twenty locations for sampling have been selected around Big and Little Glen Lakes and testing continues.

Hopefully, ongoing DNA test results can answer remaining questions and point out other factors that may help to better manage and prevent SI.

Phase V: 2020 Prevention: Based on what has been learned over the past three years about Swimmer’s Itch, we now know that the individual swimmer can prevent SI. By adjusting where, how and when we swim, we can prevent Swimmer’s Itch. The GLA will continue its research to better understand SI and try to protect the swimmer from the Itch through education about the topic.