In Chapter 1, Gumert discusses the various ways in which humans interact with long-tailed macaques, pointing out how human and macaque behaviors shape these encounters. Understanding interspecies interactions provides an indispensable backdrop for considering how infectious agents are transmitted both from humans to primates and from primates to humans (Daszak et al., 2001). It should be appreciated that, while we focus our discussion here on cross-species transmission between humans and primates, this dyadic interaction takes place within a much larger and more complex pathogen landscape that includes many other species present in the environment, as well as the environment itself, which constitutes an additional reservoir of infectious agents.
The likelihood of interspecies infectious agent transmission depends on numerous factors, including prevalence of infectious agents in the reservoir population, capacity of the potential “recipient” to sustain infection, and the manner in which species interact (Jones et al., 2008). Consider, for example, a pet monkey and its owner. Pet owners may have close contact with a pet for years. They may share food and water with their pets, allow the pets to climb on their shoulders or head, even sleep near their pet. In some cases, the monkey is considered a part of the family, interacting with other family members, neighbors, and other animals in and around the home. Intimate contact over an extended period of time provides the opportunity for the bidirectional transmission of multiple infectious agents via multiple routes.