Opportunity or catastrophe? Effect of sea salt on host-parasite survival and reproduction

Seawater intrusion caused by anthropogenic climate change may affect freshwater species and their parasites. While brackish water certainly impacts freshwater systems globally, its impact on disease transmission is largely unknown. This study examined the effect of artificial seawater on host-parasite interactions using a freshwater snail host, Biomphalaria alexandrina , and the human trematode parasite Schistosoma mansoni . Four components were analyzed to evaluate the impact of increasing salinity on disease transmission: snail survival, snail reproduction, infection prevalence, and the survival of the parasite infective stage (cercariae). We found a decrease in snail survival, snail egg mass production, and snail infection prevalence as salinity increases. However, cercarial survival peaked at an intermediate salinity value. Our results suggest that seawater intrusion into freshwaters has the potential to decrease schistosome transmission to humans. Author Summary Climate change will have numerous impacts on many systems, including host-parasite systems. One mechanism by which climate change with impact host-parasite interactions is by rising sea levels flooding coastal regions, increasing salinity in many freshwaters. Host-parasite interactions are a key component of freshwater ecosystems, but the effects of sea water intrusion on host-parasite dynamics are largely unknown. In this study, we quantify the effects of sea salt concentration on the model host-parasite system, Biomphalaria alexandrina and Schistosoma mansoni . We demonstrate a significant, negative relationship between sea salt concentration and host-parasite survival and reproduction. The increase in freshwater salinity associated with sea level rise has the potential to decrease parasite transmission and disease burden in humans and wildlife. Abstract Figure