Ecology of bacterial pathogens: from field studies in Western chimpanzees to comparative analyses in humans

Abstract

Bacterial pathogens have infected humans and wildlife throughout history, causing varying levels of harm to their hosts. Some cause mild self-limiting illness whilst others result in severe symptoms with high mortality rates. In recent times, global mortality due to infectious diseases has somewhat decreased, but bacterial pathogens still persist as an ongoing threat to both wildlife and human populations. By monitoring outbreaks in populations and attempting to understand the determinants of severe disease, we can further our understanding of the evolution of bacterial virulence and implement effective control measures for pathogens of epidemic potential. This thesis specifically focuses on investigating non-invasive monitoring methods to detect outbreaks of bacterial pathogens in wild primates, as well as the drivers of severe infections in human pathogenic bacteria. In Chapter 1, we explore the use of faecal samples as a surveillance method for detecting Mycobacterium leprae prevalence in wild chimpanzee (Pan troglodytes verus) communities in Cantanhez National Park, Guinea-Bissau. By applying a nested PCR protocol, we report positive faecal samples from two distinct chimpanzee communities. In Chapter 2, we conduct a comparative analysis to explore how pathogen ecology predicts infection severity in human pathogenic bacteria. We show that bacteria which transmit through respiratory modes cause more severe infections than environmentally or sexually transmitted pathogens. Conversely, those that transmit sexually cause less severe infections than airborne, environmental, vector-borne and directly transmitted pathogens. We also report that bacteria which primarily infect respiratory tissues and the bloodstream cause more severe infections than those which infect gastrointestinal and genital tissues. Further, pathogens that primarily infect genital tissues tend to cause less severe infection than those which primarily infect cutaneously. Finally, those pathogens that spread systemically are more likely to give rise to more severe infections. Together, these chapters provide valuable new insights into bacterial pathogen infections in both humans and non-human primates.