Interventions can shift the thermal optimum for parasitic disease transmission.

Abstract

Temperature constrains the transmission of many pathogens. Interventions that target temperature-sensitive life stages, such as vector control measures that kill intermediate hosts, could shift the thermal optimum of transmission, thereby altering seasonal disease dynamics and rendering interventions less effective at certain times of the year and with global climate change. To test these hypotheses, we integrated an epidemiological model of schistosomiasis with empirically determined temperature-dependent traits of the human parasite <i>Schistosoma mansoni</i> and its intermediate snail host (<i>Biomphalaria</i> spp.). We show that transmission risk peaks at 21.7 °C (<i>T</i>_<i>opt</i> ), and simulated interventions targeting snails and free-living parasite larvae increased <i>T</i>_<i>opt</i> by up to 1.3 °C because intervention-related mortality overrode thermal constraints on transmission. This <i>T</i>_<i>opt</i> shift suggests that snail control is more effective at lower temperatures, and global climate change will increase schistosomiasis risk in regions that move closer to <i>T</i>_<i>opt</i> Considering regional transmission phenologies and timing of interventions when local conditions approach <i>T</i>_<i>opt</i> will maximize human health outcomes.