Assembling evidence for identifying reservoirs of infection

Abstract

Many pathogens persist in multihost systems, making the identification of infection reservoirs crucial for devising effective interventions. Here, we present a conceptual framework for classifying patterns of incidence and prevalence, and review recent scientific advances that allow us to study and manage reservoirs simultaneously. We argue that interventions can have a crucial role in enriching our mechanistic understanding of how reservoirs function and should be embedded as quasi-experimental studies in adaptive management frameworks. Single approaches to the study of reservoirs are unlikely to generate conclusive insights whereas the formal integration of data and methodologies, involving interventions, pathogen genetics, and contemporary surveillance techniques, promises to open up new opportunities to advance understanding of complex multihost systems.

Figure I

Illustrative examples of reservoir–target systems. Arrow thickness denotes rate of transmission. In (A), the reservoir comprises a single source maintenance population that transmits to a nonmaintenance target population. In (B), the reservoir comprises two connected nonmaintenance populations (of which one is the source) that together form a maintenance community. In (C), the target is a maintenance population and a source of infection and, thus, is part of the reservoir. In (D), the reservoir comprises three nonmaintenance populations, together forming two minimal maintenance communities each capable of maintaining the pathogen; together, these form a larger maintenance community. In (E), the reservoir comprises a maintenance community of multiple connected nonmaintenance populations, four of which are source populations. Modified from .

Figure 1

Illustration of disease zones characterised by low and high frequencies and/or rates of transmission from an external source of infection (force of infection, x-axis) and target-to-target transmission represented here by the basic reproduction number in the target population (R₀,_T; y-axis). We note that the source of infection can be a reservoir, a maintenance population, or a nonmaintenance population. Further details of the dynamic and genetic signatures of each zone are provided in Table 1 (main text).

Figure I

Metapopulation model and definition of reservoir capacity.

Figure II

Dog population size against relative patch values (A) estimated for rabies in 75 villages of the Serengeti District, Tanzania, and their geographic location (B). Colour gradient represents patch values V_i and circle sizes (B) are proportional to dog population size.