Diseases at the Wildlife-Human Interface: Tracking Pathogen Evolution and Predicting Future Change

Emerging infectious diseases have been recognized as a major threat to humans, livestock and wildlife. Most pathogens have been studied in the context of their importance to human and livestock health and their predicted impact on economies, with limited emphasis on how diseases spill back or spill over to and from wild reservoirs. However, viruses and bacteria typically circulate among wild animals without causing major disease outbreaks. Once in anthropogenic food production or health care systems, however, these organisms are exposed to novel environments where the potential for rapid evolutionary change is great. Thus, many organisms have utilized these systems to evolve high degrees of virulence in relatively short time periods and circulated extensively to cause losses through morbidity or mortality in livestock and humans. Spillback of pathogens evolved in anthropogenic systems into wildlife has also become increasingly common, leading to morbidity and mortality in wildlife. Although spillback of such pathogens constitutes a threat to wildlife, successful return and establishment of virulent pathogens from anthropogenic to wildlife systems are relatively rare.

Encroachment of humans into remaining wilderness areas with concomitant changes in ecosystem types and land use patterns have greatly increased in recent decades. Food production systems in developed nations have high levels of biosecurity, reducing chances of repeated spread of pathogens to and from the wild. In contrast, traditional food production systems in both developed and developing countries, along with their supply and marketing chains, are identified as leading causes of emergence and spread of virulent pathogens. Furthermore, a globalized marketplace permits wide spread distribution of many of these pathogens. Thus, there are ever-increasing distributional overlaps between wildlife, livestock and humans and their pathogens at a variety of interfaces. Understanding the drivers at play, such as host-pathogen life history traits, evolutionary history, host competence, reservoir potential and environmental conditions permitting long-term entrenchment in wild systems is crucial for predicting the success of pathogens in these man-made niches. The recent emergence and re-emergence of Highly Pathogenic Avian Influenza (HPAI) of the H5 subtype serves as a good example. The Low Pathogenic Avian Influenza (LPAI) H5 or its precursors circulate within Asian poultry industries. High pathogenicity or virulence has evolved more than once within these industries, causing losses in poultry, humans and wild birds. The effort to better understand how such systems work and evolve has focused on all aspects of influenza viruses, but crucially on interfaces between humans, poultry and wildlife.

This Research Topic will focus on understanding how interactions at the human-livestock-wildlife interfaces promote pathogen evolution and spread over large geographic areas. We propose three broad objectives: (i) to identify characteristics at interfaces that promote pathogens to move between anthropogenic and wild systems; (ii) to recognize life history and evolutionary traits that predispose some pathogens to better exploit anthropogenic as well as wild systems; and (iii) to use modeling to better predict future outbreaks and propose mitigation measures.

Image Credit: Samiul Mohsanin