Diagnostics and Epidemiology of Infectious Agents in Mountain Gorillas.

Abstract

ABSTRACT WHITTIER, CHRISTOPHER ALAN. Diagnostics and Epidemiology of Infectious Agents in Mountain Gorillas. (Under the direction of Michael K. Stoskopf and Barrett D. Slenning) Infectious diseases are one of the major threats to remaining populations of free-ranging great apes. Infections from humans are a particular concern because of increasing contact between apes and human researchers, tourists, and local communities. This study advances our understanding of infectious disease risks to free-ranging mountain gorillas (Gorilla beringei beringei) by developing and utilizing improved noninvasive diagnostics to survey wild gorillas; performing serosurveys of gorillas and locally confiscated primates to identify exposure patterns; and designing a disease transmission model to better evaluate and predict pathogen spread and epidemic outcomes in the mountain gorilla population. The risk from human and any other infections to wild apes is difficult to quantify partly because of limited diagnostic sampling. Sample collection is often restricted by the challenges of sampling free-ranging apes, while sample analysis can be constrained by storage and shipping protocols that often require fresh or frozen samples. This study expands diagnostic capabilities by showing that noninvasively collected gorilla fecal samples can be stored in guanidine isothiocyanate solution at room temperature for 6 months and allow diagnostic detection of rotavirus RNA by polymerase chain reaction (PCR). Additionally it demonstrates that advanced molecular diagnostics using real-time PCR technology can be performed directly in the field thereby bypassing the need for sample preservation and shipping. This study used a portable real-time PCR instrument to detect an 87% prevalence of a Campylobacter spp. in 157 fecal samples, and to further reveal that this gorilla Campylobacter spp. appears to be a novel isolate. Using opportunistically collected blood samples, free-ranging mountain gorillas (N=57) are shown to be exposed to 19 of 37 pathogens assayed including many that are prevalent in local human populations. Evidence of exposure from local human populations is further confirmed by a companion survey of 32 confiscated gorillas and other nonhuman primates that documented cases of seroconversion associated with captivity and in some cases with only human contact, in 2 subspecies of gorillas and three species of other primates. The infectious disease outbreak model developed in this study demonstrated the importance of modeling the mountain gorilla population as a realistic network of interconnected groups. The model shows that, in the absence of humans, the known low gorilla intergroup contact rates severely restrict the spread of infection between gorilla groups. More significantly, the model suggests that even a small group of regular human visitors with limited gorilla contact can facilitate the spread of infections between gorilla groups and thereby increase gorilla population outbreak levels.