Chimpanzees are highly susceptible to diseases of human origin because of their genetic and physiological similarities with humans (Leendertz et al. 2006; Köndgen et al. 2008). Respiratory infections, polio, anthrax and scabies have all been documented in great apes. Of particular concern is Ebola virus disease (EVD), as transmission is rapid and mortality in great apes is over 90% of individuals infected. Although there is no evidence that chimpanzees were affected by the 2014–2016 epidemic in humans in West Africa, EVD killed chimpanzees in Côte d’Ivoire in the mid-1990s, and caused dramatic chimpanzee and gorilla declines in Gabon and Congo.
The frequency of encounters between chimpanzees and people is increasing as human populations expand and encroach into chimpanzee habitat. This leads to higher risks of disease transmission. The risks are typically greater for chimpanzees that live in close proximity to human communities, and which may also come into contact with human waste, including faeces.
Disease transmission risks are also exacerbated when tourists, researchers and project staff frequently come within a few metres of chimpanzees that have been habituated for research or tourism (see, for example, Leendertz et al. 2006; Hanamura et al. 2008; Scully et al. 2018).
Respiratory viruses that resulted in high levels of morbidity and mortality at Taï have been confirmed to be of human origin (ibid.), including a coronavirus. In addition, international tourists are more likely to be carrying novel diseases to which chimpanzees have never been exposed. The implementation of human quarantine and strict hygiene rules for researchers and other longer-term visitors (such as film crews) is, therefore, highly recommended (Gilardi et al. 2015; Grützmacher et al. 2018).
IUCN best practice guidelines for great ape tourism and for health monitoring and disease control in great ape populations recommend restricting the numbers of tourists and researchers visiting each day, limiting the number and duration of visits, maintaining a minimum distance of 7 metres between chimpanzees and humans, and the wearing of face masks if within 10 metres (Macfie & Williamson 2010; Gilardi et al. 2015).