Date Published: July 13, 2017
Publisher: Public Library of Science
Author(s): Benjamin T. Plourde, Tristan L. Burgess, Evan A. Eskew, Tara M. Roth, Nicole Stephenson, Janet E. Foley, Michelle L. Baker.
Pathogens that spill over between species cause a significant human and animal health burden. Here, we describe characteristics of animal reservoirs that are required for pathogen spillover. We assembled and analyzed a database of 330 disease systems in which a pathogen spills over from a reservoir of one or more species. Three-quarters of reservoirs included wildlife, and 84% included mammals. Further, 65% of pathogens depended on a community of reservoir hosts, rather than a single species, for persistence. Among mammals, the most frequently identified reservoir hosts were rodents, artiodactyls, and carnivores. The distribution among orders of mammalian species identified as reservoirs did not differ from that expected by chance. Among disease systems with high priority pathogens and epidemic potential, we found birds, primates, and bats to be overrepresented. We also analyzed the life history traits of mammalian reservoir hosts and compared them to mammals as a whole. Reservoir species had faster life history characteristics than mammals overall, exhibiting traits associated with greater reproductive output rather than long-term survival. Thus, we find that in many respects, reservoirs of spillover pathogens are indeed special. The described patterns provide a useful resource for studying and managing emerging infectious diseases.
Since the earliest documented epidemics of plague, leptospirosis, viral hemorrhagic fevers, and rabies, we have known that humans and our domestic animals can become ill after contact with other animals . Most animal pathogens can infect multiple host species, and pathogen spillover from one host species to another is common . Pathogen spillover has been defined as scenarios in which disease occurrence in a focal population depends on a distinct reservoir source that maintains the pathogen indefinitely . Thus, controlling spillover diseases is complicated by the need to manage not only cases in the target population but also transmission interfaces and reservoir populations. Broadly, a disease reservoir is the source of new cases in a target population. A better understanding of the types of species that form reservoirs will therefore facilitate the management of many emerging infectious diseases.
Pathogen spillover is a common phenomenon driving infectious disease in humans, domestic animals, and wildlife. Intuitively, one might expect that there are some features shared among reservoirs that not only enhance their ability to serve as hosts but also their tendency to be involved in pathogen spillover. While anecdotes and simple summaries indicate that rodents, bats, ungulates, and domestic animals are common sources of human disease, our analysis sought to include spillover pathogens affecting other animals as well. In addition, we aimed to account for publication biases and other attributes of the data that could skew inferences. Further, we investigated whether exceptional life history traits may underlie a mechanism by which reservoirs are associated with spillover. We find that most reservoirs of spillover pathogens include wild animals, include mammals, and are made up of a community. We found more artiodactyl and carnivore and fewer bat and primate species to be reservoir hosts than expected by chance. These findings may signify characteristics of these orders that predispose or prevent them from serving as reservoirs. High priority zoonotic pathogens are more likely to have avian reservoirs, while among pathogens with epidemic potential in the target population, primates are overrepresented despite being relatively uncommon reservoir hosts in general. Finally, compared to mammals overall, mammalian reservoir hosts tend to have faster mass-corrected life history characteristics, specifically those associated with high reproductive output rather than long-term survival.