Pathogen Transmission from Humans to Great Apes is a Growing Threat to Primate Conservation Emily Dunay, 1,2 Kathleen Apakupakul, 2 Stephen Leard, 3 Jamie L. Palmer, 2 and Sharon L. Deem 2 1 School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 2 Institute for Conservation Medicine, Saint Louis Zoo, One Government Drive, St. Louis, MO 63110 3 IT Department, Saint Louis Zoo, One Government Drive, St. Louis, MO 63110 Abstract: All six great ape species are listed as endangered or critically endangered by the IUCN and expe- riencing decreasing population trends. One of the threats to these non-human primates is the transmission of pathogens from humans. We conducted a literature review on occurrences of pathogen transmission from humans to great apes to highlight this often underappreciated issue. In total, we found 33 individual occur- rences of probable or confirmed pathogen transmission from humans to great apes: 23 involved both pathogen and disease transmission, 7 pathogen transmission only, 2 positive antibody titers to zoonotic pathogens, and 1 pathogen transmission with probable disease. Great ape populations were categorized into captive, semi-free- living, and free-living conditions. The majority of occurrences involved chimpanzees (Pan troglodytes)(n = 23) or mountain gorillas (Gorilla beringei beringei)(n = 8). These findings have implications for conservation efforts and management of endangered great ape populations. Future efforts should focus on monitoring and addressing zoonotic pathogen and disease transmission between humans, great ape species, and other taxa to ensure the health of humans, wild and domestic animals, and the ecosystems we share. Keywords: Endangered, Hominidae, Non-human primates, Zoonoses, One Health, Free-living INTRODUCTION The family Hominidae includes seven species: humans (Homo sapiens), bonobos (Pan paniscus), chimpanzees (Pan troglodytes), Eastern gorillas (Gorilla beringei), Wes- tern gorillas (Gorilla gorilla), Sumatran orangutans (Pongo abelii), and Bornean orangutans (Pongo pygmaeus). Six of these species, the non-human primates (NHP), or great apes, have experienced decreasing population trends over the last 40 years (Walsh et al. 2003; IUCN 2016a) (Table 1). Bonobos and chimpanzees are listed by the International Union for Conservation of Nature (IUCN) as endangered; Eastern gorillas, Western gorillas, Sumatran orangutans, and Bornean orangutans are critically endangered (IUCN 2016a, b). By contrast, the human population has increased to 7.6 billion with projections of 8 billion by 2025 and over 9 billion by 2050 (IUCN 2016a). This marked difference in population trends between humans and our closest rela- tives is primarily caused by anthropogenic threats to NHP, including poaching, habitat destruction, and diseases (Walsh et al. 2003; IUCN 2015; Deem 2016; IUCN 2016a, b). Correspondence to: Sharon L. Deem, e-mail: deem@stlzoo.org EcoHealth https://doi.org/10.1007/s10393-017-1306-1 Review Ó 2018 EcoHealth Alliance