ABSTRACT
Zoonosis is described as an infectious disease that is transmitted primarily from animals to humans. More than 950 of some 1,500 known pathogens have been categorized as zoonotic 1 , and, therefore, present a significant public health risk. Consequently, the World Health Organization is engaged to address the diseases caused by existing and emerging zoonoses. In addition, One Health Initiative has been launched to emphasize that both human and animal health are inextricably linked. 2 Zoonotic bacteria have assumed additional importance since more than two-thirds of all emerging pathogens during the last three decades are zoonotic in origin. These pathogens are represented by diverse taxa and are not restricted to any particular class or group of bacteria. Data from the European Union member states have shown zoonotic bacteria with high levels of antimicrobial resistance in humans, animals, and food, which is a concern for European food safety authorities. 3 Climate change may also affect the emergence of new zoonotic diseases particularly caused by pathogens whose life cycle exists partly outside of their human hosts. 4 Furthermore, effects of climate and climate changes, particularly on the vector-borne diseases, including the ones caused by the zoonotic bacteria, is a concern since rise in temperatures, precipitation, and climate-change driven changes in the animal hosts could help establish and spread zoonotic pathogens to newer geographical areas. 5 Zoonotic pathogens maintain either an ongoing reservoir life cycle in animals or arthropod vectors without maintaining a permanent life cycle in humans; in some cases the pathogens can jump the species barrier and maintain a permanent life cycle in humans, possibly not needing the animal reservoir. Figure 45.1 shows the potential for emerging new zoonotic pathogens as a consequence of increased interactions between humans, vectors, and companion and wild animals. Climate change, including higher precipitation and global warning, may also contribute to the emergence and/or enhanced virulence of zoonotic pathogens. These interactions allow species to jump hosts, get adapted and become opportunistic pathogens. The parasitic vectors and wild animals further aid in the maintenance and spread of potential zoonotic microbial agents. Zoonotic pathogens' ability to colonize human organs and their disease-causing capability varies considerably. Because these pathogens have evolved to live in multiple hosts including both vertebrates and invertebrates to maintain their enzootic lifestyle, their genomes have evolved to help them sustain life in different host environments. Some of them have a diminished ability to synthesize essential proteins because they can be acquired from the host. However, many of them retain their ability to make specific cofactors and vitamins to sustain efficient growth. These pathogens probably exploit receptors that are common in multiple hosts to colonize and/or gain entry into human hosts. Several groups of pathogens with representatives that can cause zoonotic disease are described in their own chapters in this book. In this chapter, we briefly discuss the pathogens of the following zoonotic genera: Anaplasma, Bartonella, Borrelia, Brucella, Coxiella, Francisella, and Pasteurella.
