Observed heterogeneity in the distribution of disease within populations and across landscapes is the starting point for developing mechanistic hypotheses. The observed distribution of disease results from the sequential processes of exposure and establishment, conditional on exposure, which parallel the discussion of potential and realized dispersal in ecology. However, these two processes are not directly identifiable from the distribution of infection alone and failure to identify the dominant mechanism may lead to challenges in translating patterns to novel populations. I have used experimental systems to study the behavior of insect vectors that drive differential exposure of plants to pathogens. We used experimental arrays of host plants, to study how vector foraging behavior, and thus disease risk, responded to the distribution of host characteristics. We experimentally manipulated host forage quality (i.e. the likelihood of a vector visit) and host susceptibility by manipulating plant growth stage and pre-infection with other pathogens.
Results/Conclusions
Vector foraging behavior, and thus the distribution of host exposure to pathogens, responds to both absolute and relative individual-level characteristics of hosts. The latter implies that one must consider the population and landscape distribution of host traits to calculate disease risk and that disease risk may change dynamically in response to processes that are both extrinsic and intrinsic to an epiphytotic. This conjecture should be universal to the spread of infection in plant, animal, and human hosts. From applications in human and animal health, I illustrate how predictable human behavior generates predictable, but context dependent, disease risk. Prophylactic interventions, like vaccination, seek to provide direct benefit through immunization and indirect protection by limiting the exposure of susceptible individuals. Focusing on relative risk of exposure, which can change dynamically in time, can help to more efficiently target prophylactic interventions to maximize indirect benefit relative to operational constraints.