Patterns of livestock-pathogen transmission and emergence : a framework for categorising transmission

Infectious diseases continue to cause significant financial, economic and health issues. Much work has been done on a variety of pathogens and host species with a wide range of approaches and methodologies from many disciplines, yet a full understanding of pathogen emergence has not been achieved. A greater understanding of transmission would benefit the management of control strategies, help to improve decision-making at first diagnosis of a host-pathogen interaction and possibly prevent further spread of epidemics and therefore new cases of emergence. A major gap in all these efforts appears to be a comprehensive, detailed approach for categorising pathways of transmission. Here, I develop and present a framework to categorise transmission events of pathogens. I use this framework to review the available literature on the transmission of pathogens of seven livestock species, and to derive intra- as well as inter-species transmission routes or pathways by which pathogens may emerge and infect the livestock hosts. A general dataset of the livestock pathogens was constructed, containing information on 141 bac- terial and viral pathogen species. One finds these pathogens exploit 7204 distinct transmission routes between 215 different host species. Analysis of this dataset verifies the dominance of multi- host pathogens, and suggests that non-close or indirect transmission routes tend to be associated with larger host range. The data shows the faecal-oral transmission mode is the predominant transmission pathway for livestock infection. To attempt to link features of species-scale transmission routes with emergence rates, a second dataset was constructed. This was a more detailed description of twelve Salmonella enterica serovars, and holds 1716 distinct transmission routes, llO distinct host species. One finds t.he connectedness of a host species within its network of transmission routes is associated to its po- tential for acquiring Salmonella infection. Analysis of both datasets highlights the substantial importance of anthropogenic mechanical vectors such as food and feedstuffs for the emergence of infectious disease in both humans and livestock animals. The developed framework demonstrably captures important aspects of pathogen emergence, al- though there are limitations in the quality and availability of information required to generate the datasets. The networks of transmission routes derived using this framework show common features and structural properties which may explain emergence potential. It is hoped that, by adopting this framework, the scientific community can improve the understanding of the drivers of transmission and emergence of these important pathogens.EThOS - Electronic Theses Online ServiceGBUnited Kingdo