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.