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Providing evidence to improve practice

Action: Wear face-masks to avoid transmission of viral and bacterial diseases to primates Primate Conservation

Key messages

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  • One study in Uganda found that a confiscated young chimpanzee was reunited with its mother after being handled by caretakers wearing face-masks, alongside other interventions.
  • One before-and-after study in Rwanda, Uganda and the Democratic Republic of Congo found that numbers of mountain gorillas increased by 168% over 41 years while being visited by researchers and visitors wearing face-masks, alongside other interventions.

Supporting evidence from individual studies


A study in 2009 in savanna-woodland mosaic in Niokolo-Koba National Park, Senegal found that a confiscated 9-months old female infant chimpanzee Pan troglodytes verus that was handled by caretakers wearing face-masks along with other interventions, was reunited with its mother in the wild. Four days after confiscation, the chimpanzee was released in the vicinity of its natal group, which retrieved it immediately. The author wore a surgical mask and sanitized her hands when handling the infant and its food to prevent disease transmission. The infant’s natal group was located with the aid of poachers, after which it was released close to the group. The infant was also treated for its injured eye. The study does not distinguish between the effects of the different interventions mentioned above.


A controlled, before-and-after study in 1967-2008 in tropical moist montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo found that the mountain gorilla Gorilla beringei beringei population that was regularly visited by tourists and researchers that wore face-masks to avoid disease transmission along with ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. All visitors/researchers were recommended to wear N95 masks (when available) or a surgical mask when visiting the gorillas. Gorillas were habituated to human presence as part of the ecotourism and research programmes and visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, spending only a limited amount of time with gorilla groups, ensuring that visitors/researchers were healthy, and disinfecting visitor’s/researcher’s clothes, boots etc. In addition, the population was continuously monitored by vets and gorillas received medical treatment if necessary. When gorillas died, their cause of death was clinically determined. The study does not distinguish between the effects of the different interventions mentioned above.

Referenced papers

Please cite as:

Junker, J., Kühl, H.S., Orth, L., Smith, R.K., Petrovan, S.O. & Sutherland, W.J. (2019) Primate conservation. Pages 439-491 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.