Infection outcomes depend on within-host spatial dynamics

Abstract Host-pathogen interactions can result in stochastic variation in infection outcomes, where the host survives the infection with a persistent bacterial load, clears the infection, or succumbs to death with a high pathogen load. This inter-individual variation is thought to be driven by the speed of immune activation, pathogen virulence and the ability of the pathogen to survive inside the host, but not much is known about whether inter-individual variation in infection outcome could stem from other factors, such as within-host spatial dynamics of the pathogen during infection. Hence, in this study, we used the pathogenic bacterium Providencia burhodogranariea to investigate the effect of body part and site of injection on infection outcomes in Drosophila melanogaster. Although P. burhodogranariea disseminated throughout the body as would be expected for organisms with an open circulatory system, the bacteria localized at lower levels in the abdomen compared to the head and thorax, and they were cleared more quickly in the abdomen. Furthermore, based on our empirical results in combination with a theoretical model, we suggest that terminal infections could be a consequence of damage to the thorax. Our results highlight the role that factors such as injection site and body part can influence the spatial dynamics of the pathogen, which can, in turn, drive the infection outcomes. Competing Interest Statement The authors have declared no competing interest.