A tiger at the Bronx Zoo has become the first animal in the United States to test positive for the disease associated with the novel coronavirus. The tiger’s infection is a dramatic reminder that the coronavirus originally spread from animals to people. And that it apparently can spread from people back to different animals.
SARS CoV-2’s potential for interspecies-transmission isn’t just an object of scientific curiosity. It has huge ramifications for the human species as well some of our closest evolutionary kin.
If the coronavirus affects apes the same way it affects people—that is, giving them the potentially fatal COVID-19 disease—it could drive some ape populations toward extinction.
And it might not stop there. The virus could linger in some non-human species for years after humanity defeats the current pandemic. There it might bide its time, perhaps evolving before leaping back to the human population for pandemic, round two.
As if all that weren’t bad enough, the current pandemic has disrupted the very research that could confirm how well, and to what possible ends, SARS CoV-2 moves across species.
Dave O’Connor, a professor of pathology and laboratory medicine at the University of Wisconsin-Madison, told The Daily Beast he pondered the interspecies-transmission problem as he jogged through the woods near his home recently. “Could people be giving this virus to animals in our communities?” O’Connor asked. “Would they then become reservoirs?”
In virology, a reservoir is a virus’ hiding place. Infected individuals can have reservoirs, spots in their bodies such as their eyes where a virus can hide, avoiding detection even after doctors have declared that person recovered.
Entire ecosystems also have reservoirs. For SARS CoV-2, bats are the major reservoir. Scientists suspect the current pandemic began when bats passed the virus to people, either directly or via some “intermediate” species. The point of first contact, most likely, was an illicit wildlife market in Wuhan, China.
“I think it’s pretty clear that bats are the reservoir for coronavirus diversity, and it’s quite likely that more bat coronaviruses will emerge into humans in the future,” Thomas Friedrich, a professor at University of Wisconsin-Madison’s veterinary school, told The Daily Beast.
“I do not think the circulation patterns of coronaviruses in nature are very well understood,” Friedrich added. Nor, he said, do scientists understand the risk of “anthroponosis”—that is, humans infecting other animals.
Besides the Bronx Zoo tiger, there might be some cases where that has happened. At least one dog in China reportedly caught the coronavirus from its owner. A cat in Belgium reportedly also got infected.
The dog might have been an outlier. “Some very recent experimental work suggests SARS-CoV-2 can replicate in some domestic animals like ferrets and cats but not well in others like dogs, pigs, chickens, and ducks,” Daniel Becker, an Indiana University fellow, told The Daily Beast. “However, it’s unclear whether these species could transmit the virus to humans.”
Those cases aren’t much to go on. “Most viruses have host specificity based on the ‘fit’ of a virus’ entry receptor for a particular host protein, but these sorts of interactions take a long time to unravel in the lab,” O’Connor explained. “I don’t think there’s much [or] any data on this at the moment.”
Conservationists, especially those working with non-human apes, are worried. “At this time, we cannot know if SARS CoV-2 would develop into COVID-19 disease in gorillas, or if the virus would clinically present in a similar way in gorillas,” Kirsten Gilardi, the executive director and chief veterinary officer of Rwanda-based nonprofit Gorilla Doctors, told The Daily Beast. “If it does, gorillas live in close family units with regular physical contact, so it is possible it could also spread quickly through a family group.”
Gorilla Doctors isn’t taking any chances. “It is safest to assume that gorillas are susceptible to SARS CoV-2 and take the necessary precautions to prevent transmission from humans to gorillas,” Gilardi said.
Gorilla Doctors works in Rwanda, Uganda, and the Democratic Republic of Congo, looking after the health of endangered mountain gorillas and eastern lowland gorillas in the only countries where they live.
When SARS CoV-2 began spreading, authorities in all three countries suspended tourism in the gorillas’ habitats and began requiring staff in the gorillas’ protected wildlife parks to wear protective gear, sanitize their boots, and stay at least 30 feet from the apes at all times.
Gilardi stressed that her vets, who routinely hike into the forests to check up on gorilla troops, practiced similar safety measures even before the coronavirus first surfaced. Now the vets are also practicing social distancing and frequently checking themselves for any sign of COVID-19.
They can’t afford to get sick. Not with entire species depending on them. “Our work is more urgent than ever, because we would be the first to detect changes in their health,” Gilardi said of the gorillas.
Gilardi isn’t the only one who needs to know whether the coronavirus can move across species. If people can give SARS CoV-2 to cats and cats can give it back, the current pandemic might be just the beginning of a long battle with a very clever virus.
And the virus itself prevents us from understanding its ability to leap from species to species. “With much of the country’s research enterprise on pause at the moment,” O’Connor said, “I doubt we’ll learn much more about this for at least several months—maybe longer.”