Within-host parasite interactions and the consequences of targeted drug treatment: Insights from a wild mammal system

Background/Question/Methods:

In animal populations, individuals typically play host to a dynamic, ever shifting community of parasites, and co-infection is common. Theory and empirical work have shown that interactions between co-infecting parasite species can alter disease severity, transmission and ultimately host-pathogen co-evolution, but we are just beginning to understand the significance of such interactions in natural systems. Using a wild mouse system (the wood mouse, Apodemus sylvaticus), we used longitudinal treatment (deworming) experiments as well as observational data to examine the nature and strength of within-host parasite interactions, the stability of parasite communities to perturbation, and the fitness consequences for the host of parasite community perturbation.

Results/Conclusions:

Our experiments provide evidence for dynamic competitive interactions between co-infecting nematode and Eimeria (coccidian) parasites in wild mice, which were not predicted from purely observational data. Findings suggest this interaction is local (restricted to two species sharing the same gut section), and may be driven by local resource competition. We also examined the impact of treatment on host survival, which revealed context-dependent outcomes of parasite removal, potentially influenced by parasite-parasite interactions.