There are approximately 24,000 species of parasitic trematodes (flatworms) in the world.  Yet aside from the few species that directly infect humans or livestock, we know very little about most of them.  However, with an increase in the number of diseases that are moving into humans from wildlife, it is becoming increasingly important to understand what factors regulate infection levels and disease outbreaks in wildlife systems.  Trematode systems have been understudied in this regard, but have the potential to teach us a lot about how parasites move through natural systems.  Most trematodes have complex life cycles involving multiple host species that may use landscapes at very different spatial scales.  For example, waterfowl that serve as definitive hosts may move over much larger areas than snails that serve as intermediate hosts.  In addition, varying environmental conditions can have important impacts on infection dynamics.

Results/Conclusions

In this study, we began to examine these complex influences on infection by completing a survey of trematodes in first intermediate host snails, Goniobasis spp., in 37 streams in the Upper New River Basin of Virginia and North Carolina.  Four trematodes were identified: Metagonimoides oregonensis, Sanguinicola spp., a trematode with virgulate type cercariae, and a trematode with cotylomicrocercous type cercariae.  Prevalence of these four species in the snail hosts varied immensely among sites.  To examine the land cover features that influenced the likelihood of snail infection at local and broad scales, buffers were created using a GIS around each sampling site at distances of 50m, 200m, 2000m, and 5000m. GIS analysis indicated that across all four spatial scales examined overall snail infection was negatively correlated with low-intensity development, while at the three largest distances, overall infection was positively correlated with woody wetlands.  Results for individual trematode species varied substantially, with no clear pattern present based on land-use characteristics or spatial scale.  We suspect that land-use influences individual trematode species mainly by impacting definitive host movements across the landscape.  However, further work will be required in this system to understand the complexities of these influences.