Interactions between co-infecting pathogens are common in wildlife populations and each pathogen has the potential to affect one another?s transmission. In African buffalo, disease interactions may have important social and economic consequences because buffalo are the main reservoirs of brucellosis and bovine tuberculosis. Both brucellosis and tuberculosis are bacterial infections that cause significant morbidity during spill-over infections to cattle in areas surrounding wildlife preserves, such as on the borders of Kruger National Park, South Africa. Bovine tuberculosis was only recently introduced into Kruger National Park's buffalo population in the 1980s, so its effects on both the buffalo population as well as on brucellosis transmission are unknown. Bovine tuberculosis may reduce the spread of brucellosis if it causes increased mortality in co-infected animals or may increase the spread of brucellosis if the immune suppression it causes enhances the transmission of brucellosis. This project aims to understand how the immune-suppression and increased mortality caused by Bovine tuberculosis affect brucellosis transmission. The project will combine immunological tools to investigate pathogen interactions in individual buffalo, with mathematical models to scale up from individual hosts to predict population scale consequences for disease transmission in buffalo.
This project will foster stronger linkage between veterinarians and ecologists through collaborations, and outreach in Africa and at the veterinary school at Oregon State University. Understanding the mechanisms and consequences of wildlife disease interactions requires integration between these fields as they offer different perspectives and techniques. Results from this project will have practical implications for management of wildlife diseases in general and for predicting the consequences of new pathogens in their wildlife reservoirs.
In wildlife populations, hosts are commonly infected with multiple parasites and interactions between co-infecting pathogens are ubiquitous. This research aims to understand the causes and consequences of co-infection for host survival and disease transmission. This question is particularly important in situations when host populations are exposed to new infections because it is unclear how new diseases may alter the spread of native pathogens. Because of its relevance to disease management, this project also aims to communicate the results of this work through formal presentations and collaborations with local veterinarians and managers. Specifically, this work investigates how an introduced infection, bovine tuberculosis (Mycobacterium bovis), moderates the dynamics of a similar, endemic bacterial infection, bovine brucellosis (Brucella abortus) in their reservoir host, the African buffalo (Syncerus caffer). We asked, (1) if bovine tuberculosis (bTB) alters the susceptibility to, duration or intensity (infectiousness) of B. abortus infection; (2) if immune suppression in co-infected hosts may underlie these changes; (3) and what are the consequences of co-infection for disease spread? The results of this work have resulted in a better understanding of how brucellosis is diagnosed in African buffalo (Gorsich et al. 2014, Journal of Wildlife Diseases), its epidemiology, and associations with buffalo survival and fecundity (Gorsich et al. in review). This work has shown the age and sex patterns of infection (Figure 1) and has described, for the first time, an association of brucellosis infection with reduced survival and fecundity in buffalo populations (Figure 2). The results of these analyses were written in collaboration with the scientists and managers performing disease surveillance within Kruger National Park and are either published or in review in academic journals. The analyses of how bTB alters susceptibility to and the intensity of brucellosis infection (questions 1 to 3 above), have also been completed and presented in academic settings. We have found significant consequences of bTB infection on the likelihood of acquiring brucellosis and on host survival (Figure 3). This work has also explored how the host immune response changes through the course of bTB infection. We have measured three different aspects of the host immune response. Figure 4 shows the results of one assay, which measures the host innate immune response by testing the ability of whole blood to kill bacteria. We found that animals infected with bTB or co-infected with bTB and brucellosis were associated with a lower response (Figure 4). All data collection (animal capture work and immunological assays) and presentations designed to disseminate knowledge to a non-scientific audience in South Africa have been completed for this project (Figure 5). However, we will continue to report this information in academic settings in the US and South Africa as the final results of this research are synthesized and published.
