Indirect pathogen transmission can be vectored or environmentally-mediated. The latter is the primary mode of infection for a number of important multi-host diseases in wildlife and livestock, including several zoonoses (diseases that spillover into humans) and is explicitly linked to host movements and foraging in areas where the pathogen is maintained in environmental reservoirs. Calculating R0 in such systems requires that we estimate the contribution of each reservoir to new cases. To do this we must unpack the transmission process into its pathogen shedding, environmental persistence, and host contact (pathogen ingestion or inhalation) components. Such contact rates can be characterized from a combination of local host movement and foraging patterns driven by larger-scale seasonal resource selection. Persistent environmental pathogen reservoirs can be modeled as individual, local infectious zones with their own demography and spatial distribution; life history of these zones influence host foraging locally. In this 4-year EEID project, we provide a novel combined geospatial and mathematical approach for estimating R0 for environmentally-mediated transmission. We will then assess efficacies of control strategies impacting different components of the transmission process. Toward this, we propose the following specific aims:
Specific Aim 1 : Derive functions to describe host-specific contact rates with local infectious zones by quantifying host movement and foraging behavior, characterizing the spatial distribution and demography of local infectious zones, characterizing the environmental factors controlling host foraging and pathogen persistence;
Specific Aim 2 : Apply these functions to estimating R0 for anthrax (indirect transmission of Bacillus anthracis) using empirical datasets from two regions with active anthrax in free ranging herbivores-contrasting systems with and without disease control;
Specific Aim 3 : Evaluate the conceptual and practical impact of our novel R0 estimates as related to disease control strategies for wildlife and livestock systems, including those where human disease remains a major threat.
Indirect transmission of environmentally-maintained pathogens can be controlled in multiple ways. We will produce computational tools for evaluating ways to reduce R0 in systems with long-term pathogen persistence. Our anthrax model can be extrapolated to other indirectly transmitted diseases, such as chronic wasting disease (CWD) or brucellosis; each high risk to multiple herbivorous hosts and humans.
