Searching while sick: How does disease affect foraging decisions and contact rates?

Infection often changes an animal's motivation or ability to forage, which should alter rates of contact with uninfected hosts. However, links are likely complex and remain poorly understood. Here, we explore relationships among infection, foraging decisions and contact rates and how these could interact with ecological factors to drive pathogen transmission. Under optimal foraging theory, animals should gather the highest quality resources from a patch, leaving only once the cost of continued foraging outweighs the amount of energy gained. However, the ability to locate and evaluate resources will vary with many factors, including disease, temperature and habitat fragmentation. Although modelling suggests that such variation in foraging decisions can alter contact rates among infected and uninfected hosts, and thus transmission and evolution of infectious agents, empirical studies have only begun to test the direction and strength of such relationships. We propose that foraging behaviour will often change with infection, thereby affecting contact rates, because of sickness behaviours, self-medication, parasite manipulation of the host and nonadaptive behavioural responses to infection. We recommend that future studies empirically test how such associations vary with ambient temperature and habitat fragmentation, as human activity continues to alter these environmental pressures. Furthermore, we suggest that such relationships among infection, foraging and environmental factors could help shape not only population-level disease dynamics, but also surrounding ecological communities. By revealing how environmental factors impact such links, we can improve our understanding and prediction of animal disease dynamics in the face of changing ecosystems. Read the free Plain Language Summary for this article on the Journal blog.