Year 1 Tanzanian ponds snail-parasite dynamics

Different populations of hosts and parasites experience distinct
seasonality in environmental factors, depending on local-scale biotic and
abiotic factors. This can lead to highly heterogeneous disease outcomes
across host ranges. Variable seasonality characterizes urogenital
schistosomiasis, a neglected tropical disease caused by parasitic
trematodes (Schistosoma haematobium). Their intermediate hosts are aquatic
Bulinus snails that are highly adapted to extreme rainfall seasonality,
undergoing prolonged dormancy yearly. While Bulinus snails have a
remarkable capacity for rebounding following dormancy, we investigated the
extent to which parasite survival within snails is diminished. We
conducted an investigation of seasonal snail-schistosome dynamics in 109
ponds of variable ephemerality in Tanzania from August 2021 to July 2022.
First, we found that ponds have two synchronized peaks of schistosome
infection prevalence and observed cercariae, though of lower magnitude in
the fully-desiccating than non-desiccating ponds. Second, we evaluated
total yearly schistosome prevalence across an ephemerality gradient,
finding ponds with intermediate ephemerality to have the highest infection
rates. We also investigated dynamics of non-schistosome trematodes, which
lacked synonymity with schistosome patterns. We found peak schistosome
transmission risk at intermediate pond ephemerality, thus the impacts of
anticipated increases in landscape desiccation could result in increases
or decreases in transmission risk with global change.