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A preliminary report suggests that mask wearing and social distancing may curb the spread of disease from humans to great apes.
The mountain gorillas that live in Rwanda’s Volcanoes National Park have frequent encounters with humans. On any given day, the animals might come across smartphone-toting tourists, fecal-sample-swiping biologists or antibiotic-administering veterinarians.
So when the coronavirus started spreading around the world in early 2020, experts worried that people might unwittingly pass the virus to the endangered apes, which are known to be vulnerable to a variety of human pathogens.
“In the past, other human viruses have caused respiratory illness in the gorillas,” said Dr. Kirsten Gilardi, the executive director of Gorilla Doctors, an international team of veterinarians that provides care for wild gorillas. “We were on pins and needles wondering, OK, if this virus gets into the mountain gorillas, what’s it going to do?”
In March 2020, in an effort to safeguard the animals, Rwanda temporarily closed Volcanoes National Park. When the park reopened a few months later, it had strict new precautions in place, including requiring tourists and researchers to wear masks and keep their distance from the gorillas. These rules, plus a general drop-off in tourism, mean that the park’s gorillas have had relatively few close encounters with humans during the pandemic, Dr. Gilardi said.
And so far, there have been no signs of the coronavirus among the gorillas. But in trying to control an extraordinary health threat, officials may have also alleviated a more everyday one — the routine transmission of respiratory diseases from humans to great apes. Since March 2020, the number of outbreaks of respiratory illness among the park’s gorillas has fallen to 1.6 a year, on average, from 5.4.
“The takeaway is these best-practice measures for protecting great ape populations appear to be working,” said Dr. Gilardi, who reported the findings in Nature this month. The report was co-written by Prosper Uwingeli, the chief warden of Volcanoes National Park.
The analysis is preliminary, and the researchers cannot prove that the gorillas’ health improved because humans kept their distance. But the findings suggest that even after the pandemic wanes, stricter controls may be needed to help protect endangered apes from catching diseases from people, scientists said.
“The same types of things that can protect wild animals that are susceptible to Covid can also protect them from other human pathogens,” said Thomas Gillespie, a disease ecologist at Emory University who frequently works with wild primates but was not involved in the new research.
Just over 1,000 mountain gorillas remain in the wild, divided between national parks in Rwanda, Uganda and the Democratic Republic of Congo. Many gorillas have been deliberately habituated to humans to help facilitate both research and eco-tourism.
The apes face a variety of threats, including poaching and habitat loss, but respiratory disease is also a major concern and a leading cause of death in mountain gorillas.
Outbreaks of respiratory illnesses have become common among the animals. “They happen with regularity,” said Dr. Gilardi, who is also a wildlife veterinarian at the University of California, Davis. “And we don’t always know what causes them.”
Bacteria and viruses circulate naturally among gorillas and other apes, some of which can cause respiratory infections. But scientists have also documented numerous instances in which human pathogens, including the rhinoviruses and coronaviruses responsible for common colds, found their way into great apes.
In many instances, respiratory viruses cause relatively mild, and familiar, symptoms in infected gorillas.
“They cough, they sneeze, they have runny noses, they might have goopy eyes, they might be off their feed, lethargic, literally not wanting to get out of bed in the morning,” Dr. Gilardi said. (Gorillas make, and slumber in, night nests.) “They look and act just like we do when we have an upper respiratory tract infection.”
But these outbreaks can sometimes cause severe illness, including pneumonia, or even death. In 2009, a human respiratory virus sickened 11 of the 12 gorillas in a single family group in Rwanda. Five of the animals required veterinary care and two others, including an infant, died.
To curb this cross-species disease transfer, the International Union for Conservation of Nature issued a set of guidelines in 2015 for scientists, tourists and other people who might encounter great apes. The recommendations include remaining at least 23 feet from the animals and wearing a face mask when near them. (Dr. Gilardi and Dr. Gillespie were both among the authors of the guidelines.)
But not all countries adopted, or enforced, the recommendations, Dr. Gillespie said. Until the pandemic hit. “The pandemic has really brought everyone up toward full adherence,” he said.
Volcanoes National Park now requires tourists, park personnel, researchers and other people encountering gorillas to wear face masks, which had not previously been mandated. It also requires people to remain nearly 33 feet away from the animals. Tourism has not fully rebounded either, Dr. Gilardi said.
The difference has been noticeable, she said: “We’re just not seeing as much respiratory disease right now as we have in years past.’”
Other great ape sites are currently collecting their own data on how, and whether, the incidence of infectious disease has changed since the beginning of the pandemic, Dr. Gillespie said. And the same precautions can be used to help safeguard a wide range of wild primates, he added.
“Many of these best practices can be applied very successfully to other endangered and threatened species,” Dr. Gillespie said. “People need to be doing these things Covid or not.”