Examining zebra mussel and crayfish effects on swimmer’s itch, a snail-borne parasitic disease

Abstract Swimmer’s itch is caused by avian schistosomes, snail-borne parasites that normally use birds as definitive hosts but sometimes try to infect humans. Although it is clear that higher densities of waterfowl and snail hosts lead to increased swimmer’s itch incidence, the effects of other ecological variables on these parasites are less well understood. Preliminary data collected by the Raffel lab in 2015 suggested links between urbanization and swimmer’s itch in northern MI lakes, apparently mediated by effects of increased water clarity and growth of attached algae (i.e., snail food) on snail populations. Urbanization might lead to (1) increased introductions of invasive species like zebra mussels, which increase water clarity, and (2) insecticide runoff leading to declines in crayfish, the most important invertebrate predators of snails and mussels. My project investigated relationships between abundances of zebra mussels, crayfish, snails, and avian schistosomes in MI lakes as well as environmental and habitat data, such as water temperature, algae, and substrate type, as part of a large-scale survey effort being conducted by the Raffel lab in 2016. Our findings will help to determine the causes of swimmer’s itch in northern MI lakes and inform future management efforts, so perhaps one day our kids will no longer have to worry about it.