Ecological patterns and predictors of parasite sharing among domestic and wild mammals

Abstract

Multi-host pathogens of domestic and wild mammals have significant socio-economic, animal health and conservation consequences. However, despite the interest in diseases at this interface, most research has focused on only a few key pathogens. Studies of focal systems provide limited information on the broad scale ecological patterns of pathogen occurrence and the factors that might drive these distributions, yet large scale studies may have important consequences for disease control and pathogen surveillance. This thesis aims to quantify the abundance and distribution of pathogen sharing among domestic and wild mammals, and develop and understanding of the processes that determine this distribution. Using comparative methods and comprehensive databases this thesis provides the first systematic assessment, on a global scale, of which domestic mammal pathogens have been reported in wild mammals in natural settings. Assessing the extent of pathogen sharing and the characteristics of the pathogens involved showed that the occurrence of domestic mammal pathogens in wild mammals was greater than previously recorded, with an additional 28.5% of domestic pathogens reported to infect wild hosts. Pathogens with the broadest host range had the greatest sharing probability and, in general, pathogen transmission strategies did not limit the degree of sharing. Importantly, from analysing reporting trends, the majority of shared pathogens are already likely to be known, but these are still being reported from novel host-parasite combinations suggesting that the opportunities for pathogen transmission continue to occur, especially since the majority of pathogens have been reported in wildlife multiple times. Most wild ungulates (artiodactyla and perissodactyla) have evidence of infection with domestic livestock parasites, and these hosts are also dominated by those more closely related to livestock. However, phylogenetic relatedness did not appear to be a barrier of infection. The diversity of sympatric wild species was associated with a greater proportion of shared viruses and bacteria, but a lower proportion of shared helminths. These differences among parasite groups are potentially due to variation in parasite transmission strategies. Hosts of conservation concern were not more likely to be infected with domestic mammal pathogens than un-threatened species, suggesting that domestic hosts do not directly contribute to parasite driven declines of wild mammals. Assessing the spatial reporting of wild mammal parasites and what global environmental drivers determines the occurrence of shared parasites may have important implications for disease control and surveillance. Although there are bias in reporting, the majority of wild mammal sampling locations reported pathogens also found in domestic mammals. Livestock densities did not predict the occurrence of pathogens in wild ungulates, but human densities (a proxy for domestic carnivores) did predict the occurrence of pathogens in wild carnivores. For both host groups economic variables were also informative. The probability of parasite sharing was lower in protected area systems, suggesting that these areas may have an valuable role in wildlife disease management. Pathogen sharing among domestic and wild mammals is ubiquitous. Therefore, systematic surveillance for shared pathogens or those shared pathogens that are likely to cross the species barrier in the future is arguably not beneficial. Instead, the informative drivers determined from this macro-ecological analysis, and the identification of areas and hosts that have an increase risk of pathogen sharing may help inform disease management and surveillance strategies