A novel schistosome species hosted by Planorbella (Helisoma) trivolvis is the most widespread swimmer's itch-causing parasite in Michigan inland lakes.

Cercarial dermatitis ('swimmer's itch'; SI), characterized by small itchy bumps caused by schistosome parasites of birds and mammals, is a common problem in Michigan. Research on avian schistosomes began nearly 100 years ago in Michigan inland lakes, yet scientists are still uncovering basic biological information including the identification of local snail and parasite species that cause SI. Previous research primarily focused on lakes in the northern half of Michigan's lower peninsula, although SI occurs throughout the state. We surveyed snails and snail-borne trematodes in lakes across Michigan's lower peninsula and used quantitative polymerase chain reaction analysis of filtered water samples to identify parasites to the species level, including a recently discovered parasite species that uses the snail Planorbella (Helisoma) trivolvis as its intermediate host. Most SI mitigation efforts have focused on a parasite species hosted by the snail Lymnaea catescopium ( = Stagnicola emarginata); however, lymnaeid snails and their associated schistosome species were largely restricted to northern lakes. In contrast, P. trivolvis and its associated parasite species were common in both northern and southern Michigan lakes. A third schistosome species associated with physid snails was also present at low levels in both northern and southern lakes. These results indicate that the recently discovered parasite species and its planorbid snail intermediate host may be more important drivers of Michigan SI than previously thought, possibly due to increased definitive host abundance in recent decades. These results have potentially important implications for SI mitigation and control efforts.

Efficacy of praziquantel in treating natural schistosome infections in common mergansers.

Fifty-one common mergansers were captured on Douglas Lake (Cheboygan County, Michigan) and their avian schistosome loads were determined by fecal examination. Each bird was given a single dose of 0, 40, or 200 mg/kg of body weight of praziquantel and released. All birds were recaptured within 10 days of drug administration to determine posttreatment schistosome loads. Only the highest dose of praziquantel was found to significantly reduce avian schistosome loads. The potential use of praziquantel in swimmer's itch control programs is discussed.

Hematozoa of hatch-year common mergansers from Michigan.

Fifty-five hatch-year common mergansers (Mergus merganser) were sampled for hematozoa from Douglas Lake (Michigan, USA) on 17 July 1995. Forty-one (75%) were infected with hematozoa. Haemoproteus greineri and Leucocytozoon simondi were common, infecting 28 (51%) and 26 (47%) common mergansers, respectively. Plasmodium circumflexum infected two (4%) birds. The common merganser is a new host record for H. greineri and P. circumflexum. Intensity data indicate possible negative interspecific interaction between H. greineri and L. simondi.

An apparatus for individually isolating large numbers of snails.

An apparatus for rapid screening of large numbers of snails for cercariae of digenetic trematodes is described. Snails are placed in special plastic vials suspended in Lexan inserts, exposed to fluorescent light in a wooden cabinet, and then examined in a special aluminum tray designed for use with a dissecting microscope.

Efficacy of praziquantel in natural populations of mallards infected with avian schistosomes.

In 1991, mallards (Anas platyrhynchos) on North and South Lake Leelanau in Leelanau Co., Michigan were trapped, examined for natural infections of avian schistosomes, and treated with praziquantel. Prevalence of infection from the 113 birds recaptured in 1992 was compared with that of the previous year on these 2 inland lakes after some of the birds were treated. Infections were determined by examining diluted fecal samples for hatched schistosome miracidia. Approximately 15% of the 366 birds captured the first year homed the second and made up about 27% of the resident mallard population. Of the birds treated in 1991, only 1.8% showed an infection in 1992 compared with 14.6% for previously untreated birds. These data indicate that praziquantel is an effective therapeutic agent for reducing natural infections of the parasite in mallards. Furthermore, yearly treatment of mallards at specific sites may not be necessary for effective control of swimmer's itch on North and South Lake Leelanau.