In the study of environmentally transmitted diseases, taking an ecological approach can dramatically increase our understanding of the dynamics of such diseases (e.g. cholera""""""""). In this proposal, we develop a modeling framework for the environmentally transmitted pathogen, Bacillus anthracis, the causative agent of anthrax, a deadly disease that affects mammals worldwide. We will explore this pathogen's survival in the environment, test hypothesized factors that may affect disease dynamics and integrate this knowledge using statistical and dynamical modeling techniques through the following Research Components (RC). RC 1. Spores in the environment. We will study carcasses as a source of spores in the environment and determine the role of scavengers in spreading or removing spores by experimentally excluding scavengers from carcasses. At scavenger latrines and control sites, we will use microarrays to determine the structure of the soil microbial community, including B. anthracis and characterize any changes that may contribute to the seasonality of anthrax epizootics. We will determine whether a native grass promotes replication of B, anthracis in the soil in a manipulative field experiment. RC 2. Pathogen genetics. We will study how pathogen strain type contributes to disease dynamics by strain typing anthrax-positive carcasses of any host species that were collected in the past 28 years. Using archival samples, we will determine whether different strains contribute to differences in the timing of anthrax outbreaks in Burchell's zebra (Equus burchellf) and elephant (Loxodonta africana). RC 3. Heterogeneity in host susceptibility. We will determine whether the primary host in our system, zebra, exhibit variation in genes that may influence susceptibility to B. anthracis. We will examine intra- and interannual changes in host condition and immunity in relation to potential stressors including nutrition, reproduction and lactation cycles and gastrointestinal (GI) parasite infections to determine if seasonal nadirs in host condition correlate with timing of anthrax outbreaks. RC 4. Host-pathogen dynamics and management interventions. We will integrate data arising from RC 1-3 into models describing the spatiotemporal dynamics of host populations and of B. anthracis in the environment and combine these factors in a predictive model of host susceptibility and anthrax occurrence. We will perform model fitting and selection and explore the theoretical efficacy of commonly enacted control measures.
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