Luis M. Silva , Kayla C. King, Jacob C. Koella

Parasite transmission is a complex, multi-stage process that significantly impacts host-parasite dynamics. Transmission plays a key role in epidemiology and in virulence evolution, where it is expected to trade-off with virulence. However, the extent to which classical models on virulence-transmission relationships apply in the real world are unclear. In this insight piece, we propose a novel framework that breaks transmission into three distinct stages: within-host infectiousness, an intermediate between-host stage (biotic or abiotic), and new host infection. Each stage is influenced by intrinsic and extrinsic factors to the parasite, which together will determine its transmission success. We believe that analyzing the transmission stages separately and analyzing how they influence each other might enhance our understanding of which host-, parasite- or environmental-driven factors might shape parasite evolution and inform us about new effectors to act on when designing disease control strategies.