Department of Biological Sciences, Oakland University, 118 Library Drive, 374 Dodge Hall, Rochester, MI 48309, USA Department of Biological Sciences, University of Notre Dame, 100 Galvin Life Science Center, Notre Dame, IN 46556, USA
Madelyn L. Messner
Department of Biological Sciences, Oakland University, 118 Library Drive, 374 Dodge Hall, Rochester, MI 48309, USA
Jenna Stanny
Department of Biological Sciences, Oakland University, 118 Library Drive, 374 Dodge Hall, Rochester, MI 48309, USA
Ryan B. McWhinnie
Department of Biological Sciences, Oakland University, 118 Library Drive, 374 Dodge Hall, Rochester, MI 48309, USA
Hamzah D. Ansari
Department of Chemistry, Oakland University, 146 Library Drive, 260 Mathematics and Science Center, Rochester, MI 48309, USA
Aleena M. Hajek
Department of Biological Sciences, Oakland University, 118 Library Drive, 374 Dodge Hall, Rochester, MI 48309, USA
Alexander Bageris
Department of Biological Sciences, Oakland University, 118 Library Drive, 374 Dodge Hall, Rochester, MI 48309, USA
Thomas R. Raffel
Department of Biological Sciences, Oakland University, 118 Library Drive, 374 Dodge Hall, Rochester, MI 48309, USA
Avian schistosomes are snail-borne trematode parasites (Trichobilharzia spp.) that can cause a nasty skin rash in humans when their cercariae mistake us for their normal bird hosts. We sought to investigate drivers of the spatial distribution of Trichobilharzia cercaria abundance throughout Northern Michigan lakes. For 38 sites on 16 lakes, we assessed several dozen potential environmental predictors that we hypothesized might have direct or indirect effects on overall cercaria abundance, based on known relationships between abiotic and biotic factors in wetland ecosystems. We included variables quantifying local densities of intermediate hosts, temperature, periphyton growth rates, human land use and hydrology. We also measured daily abundance of schistosome cercariae in the water over a 5-week period, supported by community scientists who collected and preserved filtered water samples for qPCR. The strongest predictor of cercaria abundance was Lymnaea host snail density. Lymnaea density was higher in deeper lakes and at sites with more deciduous tree cover, consistent with their association with cool temperature habitats. Contrary to past studies of human schistosomes, we also found a significant negative relationship between cercaria abundance and submerged aquatic vegetation, possibly due to vegetation blocking cercaria movement from offshore snail beds. If future work shows that these effects are indeed causal, then these results suggest possible new approaches to managing swimmer's itch risk in northern MI lakes, such as modifying tree cover and shallow-water vegetation at local sites.
