Emerging or re-emerging diseases in human populations have increased over the last thirty years. Since 70% of such diseases are caused by pathogens originating from animal hosts (i.e. Ebola, AIDS, and avian influenza), this increase has prompted the study of eco-epidemiological systems that occur at the interface between human and animal populations (i.e. wild and/or domestic). Contacts between hosts are particularly important factors in these systems since they result in pathogen transmission among individuals and, therefore, disease diffusion within and among populations.
We used foot-and-mouth disease (FMD) as a model to study pathogen transmission from wild to domestic populations. As the African buffalo (Syncerus caffer) is the presumed reservoir of this highly contagious disease, we examined the conditions in which the virus was transmitted to cattle sensitive to the disease (Bos taurus and Bos indicus) at the bord
ers of African national parks; these areas are interfaces between anthropogenic and protected areas in which animals can move freely.
In the context of this Ph.D., four protocols were implemented between 2010 and 2011 in Zimbabwe.
First, 36 GPS (Global Positioning System) collars were placed on cattle and buffalo in order to describe and analyze cattle their movements across the landscape as well as to quantify interspecific contacts. In one of the study sites, eleven collars were attached to one of the predators of these ungulates: the lion (Panthera leo). By integrating the predator guild into our telemetry protocols, we could examine the potential changes in spatial use by cattle and buffalo in response to predator presence and their consequences for contact dynamics and interspecific pathogen transmission.
Second, a longitudinal serological survey was conducted in which tagged individuals were sampled repeatedly over the course of different seasons. Anti-FMD antibodies were detected using ELISA.
Third, to characterize contacts within the domestic host population, interviews were conducted with cattle owners regarding their husbandry practices across seasons (i.e. descriptions of grazing and watering areas as well as herd mixing).
Fourth, to describe the potential role of host diversity in ecosystem infection risks, macroparasite density (i.e. ticks) was estimated for landscape compartments that contrasted in terms of potential hosts present (i.e. (i) wild, (ii) domestic and wild, and (iii) domestic only).
Our study primarily shows the following results. (1) Interspecific interaction rates, as estimated by telemetry, vary between sites and have a pronounced seasonality (peak occurs during the hot dry season). (2) Resource distribution (i.e. water and grazing areas) seems to condition the frequency and distribution of these contacts in the different landscape compartments. (3) Cattle incursion frequencies into protected areas and the frequency and intensity of contact with buffalo significantly positively affect the probability of foot-and-mouth antibody acquisition in cattle. The probability of antibody loss in cattle is also a function of diminished rates of interaction with buffalo. (4) Intraspecific interaction densities positively influence FMD serological incidence in cattle. (5) Top predator presence in the landscape could limit cattle incursion into protected areas and reduce the likelihood of their being infected by wild host populations. (6) Finally, the estimated densities of two macroparasite genera, the ticks Rhipicephalus sp. and Amblyomma sp., in the vegetation were higher in communal spaces where there was no interaction with wild hosts and where host species richness was weak.
The results of this study on the interspecific transmission of pathogens between wild and domestic populations in tropical ecosystems encourage the exploration of research topics that are still largely unexplored, including the evolution of virulence transmission modes of pathogens hosted by sympatric wild and domestic populations. Individual control mechanisms deployed against pathogens (i.e. immunity resulting from natural exposure and/or vaccination) are also discussed in this thesis. Finally, this work generates questions about biodiversity’s role in species interactions and its potential dilution or amplification effects on macroparasite abundance.