In the not-too-distant past, infectious disease was viewed as akin to fire, earthquake, and tornado in its propensity to impact wild primates. Outbreaks were considered inherently unpredictable, “sweeping through” primate populations, wreaking havoc, and then subsiding. Primates were generally thought to rebound, such that the overall effect was a “blip on the radar,” a transient reduction in population numbers.

The last approximately 10 years have demonstrated the “disease as natural disaster” paradigm to be woefully inaccurate. Infectious disease has emerged as a major threat to primate conservation. The case of Ebola virus and its devastating effects on chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla) in Gabon and Congo is perhaps the most dramatic example, with some estimates of local population declines above 80% (Leroy et al., 2004; Bermejo et al., 2006). Other pathogens such as Bacillus anthracis (the causative agent of anthrax), polio virus, and yellow fever virus have also caused epidemic mortality in apes and monkeys, to the extent that they are now seen as important drivers of primate population declines (Chapman et al., 2005; Leendertz et al., 2006; Nunn and Altizer, 2006).

Despite these dramatic examples, the majority of primate pathogens probably exert chronic, sublethal effects on primates in the wild (most parasitic protozoa, helminths, and arthropods probably fall into this category). Although researchers are paying increasing attention to such agents, most studies to date have been either “prevalence surveys” or comparisons of prevalence across locations or habitat types.