Nadia had a cough. A dry cough, to be specific, and it wasn’t just her. The 4-year-old Malayan tiger lives in an exhibit in the Bronx Zoo with her sister, Azul, who had also started coughing at the end of March. Altogether, seven of the zoo’s big cats appeared ill, two Amur tigers and three African lions in addition to Nadia and Azul. They neglected their meals. They wheezed. And they worried their keepers. Fears over the spread of the coronavirus had already led the zoo to close its doors to the public starting in mid-March. Once Nadia and the other cats began showing symptoms, the remaining staff wanted to find the source of their malaise.
“Nadia was not coming around and was getting a little worse, so we anesthetized her in order to treat her,” Bronx Zoo veterinarian Paul Calle says. “We did x-rays and ultrasounds. We did blood work. We ran lots of tests, panels for normal domestic cat infectious diseases.” Although the Covid-19 pandemic had hit humans living in areas around the zoo hard, it wasn’t initially assumed to be the likely culprit. After all, no animal in the United States had been known to catch the disease. It wasn’t even clear a tiger could contract it. But with so many cases in the city, the team decided to test for SARS-Cov-2, the coronavirus that causes Covid-19, just to be sure.
Within a few days, Nadia had tested positive, making headlines as the first animal in North America to do so. The news that a tiger in New York had caught the coronavirus was eye-catching. Who the hell did a tiger know to get tested so quickly?
While New York has the highest number of confirmed Covid-19 cases in the world, it also has a test shortage, and most people experiencing symptoms live in uncertainty. Sick people who do not require immediate hospitalization have been encouraged to stay home, assume they’re infected, and wait things out. This is a frustrating and scary experience. So the news that a tiger could somehow definitely and swiftly obtain a test provoked indignation, as the care and attention shown to one animal contrasted so sharply with the neglect so many New Yorkers have felt.
The veterinary diagnosticians involved are quick to point out that the tests for the tiger were developed specifically in their labs to use on animals, so Nadia was not given a test meant for a human. And while it’s an unexpected development, the tiger’s infection is relevant for scientists trying to understand Covid-19. “Since the beginning, we’ve known that this is a disease that started off in animals and spilled over to people,” says Casey Barton Behravesh, the director of the One Health office for the Centers for Disease Control and Prevention’s National Center for Emerging and Zoonotic Infectious Diseases. “It'll be important for people working on human health and animal health issues to exchange information.”
While the exact origins of the coronavirus that causes Covid-19 are still unknown, it is believed to have originated in bats and then to have jumped to humans via a Chinese market specializing in fish and meat, including live animals. It is on its most basic level a disease that requires both animal and human health specialists to understand. Testing a tiger might sound like a bizarre detour, but it is intimately intertwined with efforts to learn about how Covid-19 impacts humans as well as animals. This is especially true because the Bronx Zoo's working theory is that a zookeeper may have accidentally infected Nadia. While a few dogs in Hong Kong, a cat in Hong Kong, and a cat in Belgium have reportedly tested positive for Covid-19 after human exposure, it is still not at all clear how easy or common it is for humans to give the infection back to the animal world, or what that might mean.
Because the tiger’s well-being is now enmeshed with a public health crisis, there are plans to conduct contact-tracing on Nadia. “The New York City Health Department is actively investigating the tiger situation further,” Barton Behravesh says.
“The Health Department will investigate. Right now this appears to be human-to-cat transmission, however, how that transmission occurred is something we still need to learn,” Department of Health press secretary Patrick Gallahue confirms. To do that, Gallahue adds, the department will interview the zoo’s staff to find out the level of contact between people and animals, and try to determine when those contacts occurred. Like so much about this pandemic, it’s an unprecedented investigation.
“This is a disease nobody knows about. Nobody has spent their lives studying this. There aren't labs dedicated just to this disease. We need to all work together and collaborate across states, across countries, across specialties to be able to get the answers that everyone needs to be able to fight this virus effectively and efficiently,” says Sam Sander, a wildlife veterinarian at the University of Illinois Veterinary Diagnostic Laboratory. “There's also opportunities for vaccine development, for additional testing, for getting more specific with how this virus replicates and when it mutates.”
Nadia actually tested positive for Covid-19 three times.
After she was peacefully knocked out, the Bronx Zoo collected samples from her nasal cavity, the back of her throat, and her trachea. The samples were then sent in duplicate to Cornell University and the University of Illinois’ veterinary labs, where they were processed immediately.
“We used a similar molecular test as the human test,” says Leyi Wang, the veterinary virologist who created the test used on Nadia’s samples at the University of Illinois. (When asked if his test could work on samples from people as well as animals, he said it could in theory, but “policy does not allow us to test humans.”) So far, in addition to Nadia, Wang’s lab has also tested a gorilla, a chimpanzee, a cat, a dog, and an armadillo. “But we only had a positive from the tiger,” he says.
Once the results came back presumed positive, the lab sprang into action to get them independently confirmed. “Our director for the lab, Dr. [Richard] Fredrickson, actually drove the samples himself to Ames, Iowa, to get the confirmatory testing by the USDA’s National Veterinary Services Laboratories. He left here at 3 am,” Sander says. The national lab began working on the sample when it arrived later that morning, and the results were back by that same evening, April 4. By April 5, the news was public.
As those headlines spread, many wondered why, with so many humans sick and wondering about their status, officials would opt to test a tiger. Others wondered something else: What does this mean for the coronavirus spreading to other animals? What does it mean for pets?
Veterinary diagnostic labs across the country are developing their own tests for Covid-19, and many use the same basic processes that human tests do. They tend to use a technique called RT-PCR (reverse transcriptase polymerase chain reaction) to analyze the samples and then look for genetic sequences that match the virus's own genes. This was the method used to test Nadia’s samples and to confirm the testing at the NVSL. “The test is performed to try and identify specific gene targets,” USDA public affairs director Lyndsay Cole told WIRED by email, noting that the CDC provides gene targets for laboratories to use.
Tim Baszler, executive director of the Washington Animal Disease Diagnostic Lab, didn’t work on Nadia’s samples, but his lab has created its own version of the test primarily aimed at pets. “We developed the test at the request of King County Public Health,” Baszler says. “They were uncertain about animals in multicare facilities for the aged when the pandemic was really hitting Seattle hard.” Baszler stressed that the actual procedure of determining whether an animal had a coronavirus wasn’t new. “What's new about this is the disease.”
When people say “the coronavirus” nowadays, they are almost always referring to Covid-19, but there are countless coronaviruses that infect animals. Humans also get other coronaviruses: SARS, MERS, and even the common cold are all members of the coronavirus family. “Horses have coronaviruses, cattle have coronaviruses, swine have coronaviruses, chickens and turkeys have coronaviruses,” says Ann Hohenhaus, a staff doctor at New York’s Animal Medical Center. “They’re widely spread throughout the animal world.”
Idexx, a commercial veterinary diagnostic lab, developed its own Covid-19 test for animals in February and has since tested more than 5,000 samples, primarily cats and dogs, along with a few horses. (Thus far, none of the samples has come back positive for Covid-19.) Jim Blacka, an Idexx veterinarian, emphasized that the prevalence and variety of coronaviruses in the animal world is another reason why tests developed for animals aren’t appropriate for humans. In fact, some of the tests are only suitable for certain species. “The test that we use is animal specific,” Blacka says. “We needed to make sure we developed a test that didn't cross-react or give us false-positive tests for other coronaviruses that weren’t Covid-19.”
Cats are extremely susceptible to a type of coronavirus that impacts the GI tract, for instance. Hohenhaus estimates that as many as 80 percent of cats get this “extremely common” strain. “It causes mild diarrhea; it doesn’t make them very sick,” Hohenhaus says. Most coronaviruses stay within species—a horse isn’t likely to catch a pig’s virus, for example. There are four main sub-groups—alpha, beta, gamma, and delta. Cats are not typically susceptible to beta-coronaviruses, like the one that causes Covid-19, which makes the fact that Nadia does appear to have been infected especially odd; it also provides more evidence that this disease is sometimes wildly unpredictable.
Currently, there are more than 1.5 million Covid-19 cases worldwide, and more than 100,000 deaths. The majority of those infected will likely recover. The big cats at the Bronx Zoo, it seems, will too. “Nadia and the other tigers and lions are doing much better,” Calle says. “We expect them all to make full recoveries.” The zoo plans to continue sharing information about the case as it comes in.
While so much is still unknown about Covid-19 and animals, all of the veterinary experts WIRED spoke with were adamant that pet owners do not need to fear infections from their pet, just because a tiger appears to have been infected. “There is absolutely no evidence whatsoever—worldwide, period, at all—that shows that cats can give the infection to people,” Sander says. But, she adds, “there is some suggestion, very preliminarily, that we potentially could give the infection to a cat, and potentially ferrets also.”
For this reason, people who have Covid-19 are encouraged to have someone else act as the primary caretaker for their pets while they self-isolate, if that is a possibility. But they don’t have to completely shun their animals in order to protect them, as the natural infection rates appear rare. “If you think about the number of people who have cats in the world, and the number of people who have been infected with Covid-19 in the world,” Sander says, “to only have a handful of cats that have shown signs of potential infection shows us that this virus doesn't very efficiently transfer into those species.”
Even if a companion animal were to contract Covid-19, it’s highly unlikely that recommendations would ever push for removing the pet from its owner. “There's great sensitivity to the human-animal bond,” Baszler says. “With Covid-19, people have anxiety enough without taking their pets away.” (Good news for all those folks out there adopting pets during the pandemic.)
Researchers are experimenting with how these animals respond to infection in a controlled setting. “What we're seeing right now is cats, ferrets, and golden hamsters are shown to be able to be experimentally infected with this virus, with very high doses of the virus in a laboratory setting,” Barton Behravesh says. Just like studying Nadia, these tests may prove revelatory about the nature of the infection. But, again, they are no cause for alarm, and they are a parallel but distinct project from human testing.
“The message I would share is don't give up your pets and don't give up on your pets,” Blacka says. “They certainly can be a source of support for all of us during these unique times, not another source of stress or anxiety.”
Updated 4-15-20, 4:30 pm EST: This story was updated to correct the spelling of Tim Baszler's name.
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