Diet of schistosome vectors influences infection outcomes

Resource availability can alter infection outcomes through its impact on host immunity and on parasite reproduction. On one hand, enhanced nutrition could favor immunity, limiting the parasite, and on the other hand, it could favor establishment and reproduction of the parasite. Our study aimed to determine the effect of diet on (1) host susceptibility to infection and (2) parasite production in a snail-trematode system. We fed Biomphalaria sudanica, a snail vector of Schistosoma mansoni, either a strict lettuce (low nutrient) or pellet (high nutrient) diet for two generations before exposing them to S. mansoni. We used two parasite strains, one that is incompatible with the snails and one that is compatible with the snails. We found that when exposed to incompatible parasites, diet did not affect snail susceptibility significantly as few snails were infected overall. However, when challenged with the compatible parasites, snails fed the high-nutrient diet were more susceptible to infection than their low-nutrient-fed counterparts. The high-nutrient-fed snails also produced more cercariae than low-nutrient-fed snails, but this advantage was lost after the initial assessment at 8 weeks. Snails that obtained infections were either kept on their initial diet or switched to the other diet. This experiment showed that snails switched from a low-to-high-nutrient diet produced more cercariae than those remaining on the low-nutrient diet and similar numbers to those remaining on the high-nutrient diet. Unexpectedly, the reciprocal diet switch (high to low nutrient) initially resulted in more cercariae relative to controls, but the pattern reversed after initial assessment. This study showed that available resources can impact the susceptibility of the vector host and the reproductive capacity of the parasites, with higher nutrients favoring parasite establishment and reproduction, highlighting the plasticity of susceptibility phenotypes, which also have a strong genetic basis. These data can aid predictions of how future environmental changes and resource availability may impact parasite transmission.