Resource fluctuations inhibit the reproduction and virulence of the human parasite Schistosoma mansoni in its snail intermediate host

Resource availability can powerfully influence host-parasite interactions.
However, we currently lack a mechanistic framework to predict how resource
fluctuations alter individual infection dynamics. We address this gap with
experiments manipulating resource supply and starvation for a human
parasite, Schistosoma mansoni, and its snail intermediate host to test a
hypothesis derived from mechanistic energy budget theory: resource
fluctuations should reduce schistosome reproduction and virulence by
inhibiting parasite ingestion of host biomass. Low resource supply caused
hosts to remain small, reproduce less, and produce fewer human-infectious
cercariae. Periodic starvation also inhibited cercarial production and
prevented infection-induced castration. The periodic starvation experiment
also revealed substantial differences in fit between two bioenergetic
model variants, which differ in their representation of host starvation.
Simulations using the best fit parameters of the winning model suggest
that schistosome performance substantially declines with resource
fluctuations with periods >7 days. These experiments strengthen
mechanistic theory that can be readily scaled up to the population level
to understand key feedbacks between resources, host population dynamics,
parasitism, and control interventions. Integrating resources with other
environmental drivers of disease in an explicit bioenergetic framework
could ultimately yield mechanistic predictions for many disease systems.