A tiger at the Bronx Zoo in New York has surprised keepers by testing positive for SARS-CoV-2. The discovery has raised alarm about the potential vulnerability of a wide array of animals, but it does not necessarily mean the same animals pose a threat to people.
Four tigers and three lions at Bronx Zoo all developed a dry cough in recent days. Zookeepers were initially skeptical that SARS-CoV-2 was the cause, and were reluctant to go through the difficult processes required to test a big cat for the virus (you try sticking a swab up a tiger's nose).
However, Nadia, a 4-year-old Malayan tiger, needed to be anesthetized for other reasons, so, as the Zoo explained in a statement: “Out of an abundance of caution,” Nadia got tested while she was in no position to object.
The National Veterinary Services Laboratory confirmed Nadia's positive status, making this the first known case of a non-domesticated animal with COVID-19 symptoms. The Zoo's Chief Veterinarian Paul Calle assured National Geographic, "It is not the same type of test that health care providers give to people, so there is no competition for testing between these very different situations.”
The source of the infection has been attributed to an asymptomatic zookeeper, who also had contact with the other coughing big cats. However, “None of the zoo’s snow leopards, cheetahs, clouded leopard, Amur leopard, puma or serval are showing any signs of illness,” reports The Wildlife Conservation Society, which runs Bronx Zoo.
Bronx Zoo has reported taking increased steps to prevent transmission between humans and animals, in either direction. Other zoos, already on lockdown to prevent humans from infecting each other, are following suit.
However, as Netflix docuseries Tiger King has made isolators aware, most of the big cats in captivity in America are not in public zoos. They're owned privately as pets or held by people whose approach to wildlife care might charitably be described as eccentric.
Neither the lions nor tigers at Bronx Zoo appear to be in serious danger, with some loss of appetite being the only reported symptom besides coughing. However, since we know most humans infected with SARS-CoV-2 experience only mild symptoms, a sample of seven is insufficient to tell us whether the disease is less severe in Panthera, or if these individuals happened to be at the lower end of the vulnerability scale.
Like most of the new infectious diseases that suddenly appear to plague us, COVID-19 came from animals, although the popular story that transference was from a human eating a bat is not necessarily true. Consequently, it's no surprise that some other non-human species can also get infected, but we're just starting to know which ones.
When veterinary evidence suggested dogs were immune the world celebrated with this joke:
There have since been disputed reports of dogs catching COVID-19, although it appears to be very rare.
At least one housecat has caught the virus, so the fact its bigger relatives can do the same shouldn't have been a total surprise. A not-yet peer-reviewed study has reported house cats can get the virus and transmit it to other cats, but none of the felines observed appeared to suffer. Moreover, the researchers deliberately tried to infect the cats by squirting large doses up their nostrils, leaving open how likely infection would be in more realistic situations.
The WHO's current advice on the topic reads: “There is no evidence that a dog, cat or any pet can transmit COVID-19.”
Some diseases can cross the species barrier in one direction, but not necessarily in the other. Cats caught the original SARS coronavirus that caused the 2002-2003 outbreak from humans, but it remains unknown if any came back the other way.
"Far and away the biggest threat to humans is other humans," Professor Glenn Browning, Director of the Asia-Pacific Center for Animal Health told IFLScience.
He noted cats appear to transmit to others of their species poorly even when cooped up with them in small cages 24 hours a day, and are even less likely to pose a threat to humans. Those animals that are particularly susceptible, like ferrets, which Browning says appear to share similar respiratory diseases receptors to humans, seldom circulate widely enough to pose a threat.
The Bronx Zoo will be sharing their diagnostic data with other zoos and scientists worldwide. The concern is if the coronavirus can jump into big cats in captivity, how might that affect populations in the wild?