An integrated account of the study of pathogenesis encompassing both the medical and veterinary fields. Discusses interactions between the individual host and the parasite, with emphasis on the parasite throughout. Briefly describes the various host defences and responses to infection, and considers the differences in susceptibility of various animal hosts as well as the differences between individuals of the same animal species. Discusses the topic of epidemiology from a microbiologist's point of view, addressing the ecology of the microbial pathogen, its natural history, and the effects produced by the outbreak at local or international levels. Also includes discussions of brucellosis, and the epidemiology of mycological diseases.