Respiratory illness outbreaks among wild mountain gorillas in Volcanoes National Park have declined since the start of COVID-19, according to a "Correspondence" report by authors from Gorilla Doctors and from the Rwanda Development Board in the journal Nature. Mountain gorillas are susceptible to human-transmitted respiratory pathogens, with respiratory illness being the second leading cause of death in wild, human-habituated populations.

In the five years prior to March 2020, the Volcanoes National Park gorilla population averaged 5.4 respiratory illness outbreaks annually. In contrast, from March 2020 through December 2021, this population averaged 1.6 respiratory illness outbreaks each year. To date, SARS-CoV-2 has not been detected in samples collected from mountain gorillas with respiratory illness. This decline in respiratory illness outbreaks during the COVID-19 pandemic correlates with an overall reduction in the number of people coming into close proximity with the gorillas, and with additional health protection measures taken to reduce the risk of disease transmission from humans to gorillas. "Respiratory illness outbreaks are common in wild, human-habituated mountain gorillas, and considering that gorillas are susceptible to SARS-CoV-2, this preliminary analysis is such a welcome finding,” said co-author Kirsten Gilardi, executive director and chief veterinary officer for Gorilla Doctors, and the director of the Karen C. Drayer Wildlife Health Center at the UC Davis School of Veterinary Medicine. "It is a testament to the early and decisive action of park authorities to help protect mountain gorillas and humans."

The additional safety measures are in accordance with the IUCN Best Practice Guidelines for Health Monitoring and Disease Control in Great Apes, which state: "... disease prevention should be regarded as a top priority ... programs should be centred on monitoring health parameters, and modifying human activities accordingly, in order to reduce the risk of disease transmission to great apes.” (Gilardi et al. 2015)

Gorilla ecotourism was temporarily suspended at the start of the COVID-19 pandemic. The Rwanda Development Board mandated mask-wearing at all times when in close proximity to gorillas and increased the minimum distance from 7 to 10 meters, or nearly 33 feet.

Jean Bosco Noheri, a Gorilla Doctors field veterinarian who compiled the data for this comparison, cites other potential correlating factors to consider as additional lines of inquiry. "Variation in pathogenicity of viruses, gorilla group dynamics, climate conditions and a variety of other factors may also be impacting the decrease in respiratory illness outbreaks we have seen," Noheri said.

These findings illustrate the imperative for following best practice guidelines that minimise human disease transmission to great apes. Particularly in light of the omicron variant surge and the return of gorilla tourism, Gorilla Doctors and the Rwanda Development Board recommend these measures be made permanent.

Adapted from the Gorilla Doctors blog

References
Gilardi, K. & Uwingeli, P. (2022): Keep mountain gorillas free from pandemic virus. Nature 602, 211
Gilardi, K. V. et al. (2015): Best Practice Guidelines for Health Monitoring and Disease Control in Great Ape Populations. Gland, Switzerland (IUCN SSC Primate Specialist Group)
Palacios, G. et al. (2011): Human Metapneumovirus Infection in Wild Mountain Gorillas, Rwanda. Emerging Infectious Diseases 17 (4), 711-713