DIBYANGSHU SARKAR/AFP via Getty Images

Zoos and aquariums might be closed to the public because of coronavirus, but the animals still need to be fed and cared for by staff. And it’s this continual close contact that may have allowed the virus to leap from humans back to animals.

Nadia is a four-year-old female Malayan tiger at Bronx Zoo in New York who tested positive for coronavirus in April, the first known infection in any tiger in the world and any animal in the US. Three more tigers living in the same enclosure and three African lions also developed a dry cough, but weren’t tested because big cats need to be sedated to take the necessary diagnostics tests and blood samples before sending them off to veterinary labs that don’t handle human samples.


The Wildlife Conservation Society (WCS), which manages the Bronx Zoo, says the female tiger was tested for precautionary reasons after zookeepers and veterinarians noticed symptoms of respiratory illness. “[They] collaborated with health departments and laboratories in the region to test for Covid-19 knowing it would be important for our global understanding of Covid-19 to confirm whether or not the animals were infected with the virus,” said Amanda Fine, associate director of WCS’s wildlife health programme in a statement on April 6.

A zoo’s design in principle keeps big cats in their outdoor enclosures for display and safe away from other animals that they would devour in an instant. Although Bronx Zoo has been closed to the public since March 16, the tiger was likely infected by an asymptomatic zookeeper handling the animal and her food. Zookeepers generally approach animals from inside areas made up of metal bars and concrete walls for feeding. As a result, it’s possible that Nadia and the other tigers and lions became infected with the virus after close contact with a contagious person.

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Staffers who handle the cats at the Bronx Zoo will now be wearing protective clothing, as primate keepers have done for years because of their close genetic similarity to humans and susceptibility to colds, flu and other disease transmission. “The animals we’d be most concerned about before this report of the lions and tigers are the big primates, especially the great apes – gorillas, chimps, bonobos and orangutans,” says Martin Whitehead, director of Chipping Norton Veterinary Hospital, who has treated zoo animals and exotic pets such as reptiles and birds. As much as a third of Africa’s wild gorillas and chimpanzees, which are highly social animals, are thought to have died from Ebola since the 1990s.

In response to the coronavirus outbreak, zoos in the UK have started social distancing to protect their animals. Zookeepers at ZSL London and Whipsnade Zoos are wearing masks and gloves while preparing animal food, and antibacterial foot dips outside enclosures and the on-site veterinary hospital help prevent the potential spread of disease. At countryside zoos some staff are living on site and away from their families.


Zoos are where most people get up close with big cats and great apes. They provide shelter for threatened species and entertain and educate visitors, especially children, but these close animal encounters are not without risk. In 2009, a human respiratory disease broke out in a group of 30 chimpanzees housed at Chester Zoo, killing three apes. Besides viral diseases, outbreaks of salmonella and E. coli bacteria found in animal waste are not only ailing food farms but petting zoos. In 2019, a toddler died of E. coli infection and three other children aged between two to 13 became ill after petting farm animals at a San Diego fair.

Bovine tuberculosis (TB) is another infectious disease caused by bacteria that is devastating beef and dairy farmers in Britain. “The outbreak that’s causing zoos a problem at the moment, other than Covid-19, is TB,” says Whitehead. “There are several zoos around the country who are literally under restrictions in the same way that farms are when they are found to be TB positive.” Paignton Zoo in Devon, for instance, was not allowed to breed or move animals to other zoos from 2017 to 2019 after an antelope tested positive for bovine TB and an Asiatic lion had to be euthanised because it became ill, probably after eating an infected cow carcass.

But just because a tiger at Bronx Zoo contracted coronavirus doesn’t mean other animals will need to be tested – yet. Cats, both wild and domestic, are known to harbour feline coronaviruses which can cause a highly fatal disease called feline infectious peritonitis (FIP), but until recently it was unknown whether they could contract Sars-Cov-2, the virus which causes the novel disease.

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In an experimental study published in Science on April 8, researchers from China’s Harbin Veterinary Research Institute injected the new coronavirus into the noses and beaks of a number of domestic animals, namely cats, dogs, ferrets, pigs, chickens and ducks, and kept them in a room with uninfected individuals of their own species. The ferrets and cats became infected with the virus and the other animals appeared not to be vulnerable. The authors of the study also say the cats showed no symptoms and developed antibodies against the virus – making them a good candidate to test vaccines and treatments that are currently in development for humans.


However, the lab experiment also raises questions. While both domestic cats and big cats seem to be able to catch the virus, there is so far little evidence of transmission between pets and their owners. That is, for one thing, because the experiment did not mirror the way people interact with their pets and how coronavirus may spread in real life.

“They were challenging the cat with vast quantities of virus, way more than we’d expect a cat in a normal household to come into contact with,” says Sarah Caddy, a vet and clinical research fellow at the University of Cambridge, who was not involved in the study.

In late March, a domestic cat in Belgium developed Covid-19 symptoms – diarrhea, vomiting and respiratory issues – about a week after its infected owner returned from a trip to northern Italy. The owner then sent off a vomit and stool sample to vets at the University of Liège where they detected the genetic material of Sars-Cov-2. The standard tests for coronavirus, however, do not detect “live” virus particles so it could be that the cat ate contaminated food and the virus simply passed through its gut without replicating.

The emerging reports of human-to-cat transmission are likely isolated cases. After all, there are millions of pet cats worldwide and, in the US, between 5,000 to 10,000 tigers are kept in roadside zoos, county fairs and private homes. With more than 1.5 million confirmed cases of infection in humans as of April 10, we’d expect more animals being reported ill. “We would know by now if this is causing significant disease in animals or if animals were actually involved in the spread of the disease,” says Caddy. For now, an animal coronavirus outbreak remains the least of our worries.

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