A new study shows that schistosome transmission can actually be highest when freshwater snail populations are low. This study demonstrates how the size of a freshwater snail population relates to its parasitic infection rate.

A new study led by Emory University, however, shows that schistosome transmission can actually be highest when freshwater snail populations are low. The Proceedings of the National Academy of Sciences published the study, the first to demonstrate how the size of a freshwater snail population relates to its parasitic infection rate.

«We’ve shown that the more snails you have in a freshwater source, the less dangerous each individual snail is, in terms of the number of parasites they’re releasing,» says David Civitello, an Emory assistant professor of biology and lead author of the study. «The incredible strength of our finding is that we’ve demonstrated the effect both in the field, using natural transmission sites, and in an experimental context, through outdoor laboratory experiments.»

The research carries important implications for policies aimed at reducing the transmission of schistosomiasis. Considered one of the most significant of the neglected tropical diseases, the parasites that cause schistosomiasis currently infect more than 200 million people.

«Our results suggest that if you apply a heavy dose of pesticides to reduce a snail population, the infectivity of the remaining snails might actually skyrocket,» Civitello says. «It’s basically impossible to kill every snail and so you set the stage for a rebound in infection risk. As the snail population begins to recover, our data tells us that this is a time with extremely high potential for transmission of the parasites to humans.»

Previous laboratory experiments had found that when an individual freshwater snail infected with the parasite is well fed, it can generate as many as thousands more parasites per day compared to an underfed snail. In fact, an underfed infected snail may generate as few as a single parasite per day.

Story Source:
Materials provided by Emory University. Original written by Carol Clark. Note: Content may be edited for style and length.