Tigers and Lions, but Probably Not Dogs
Many questions remain about which animals are susceptible to Covid-19
A four-year-old Malayan tiger at New York City’s Bronx Zoo has tested positive for the coronavirus, AP reported yesterday. The tiger, named Nadia, had exhibited a dry cough since March 27, and a group of six other tigers and lions with suspected infections were wheezing and had lowered appetites. Zoo officials believe that Nadia and the other cats were infected by one staff member who was infected, but asymptomatic.
The discovery complicates what little we know about Covid-19 and its ability to infect animals. We do know that it’s a zoonotic (animal-to-human) disease — one that originated in an animal host (likely bats) and developed the ability to spread to humans. But in addition to Nadia’s case, there’s only a handful of anecdotal evidence showing that human-to-animal transmission is possible: a housecat in Belgium, and a pomeranian and a German shepherd in Hong Kong, all suspected to have caught the virus from their owners. Some scientists have raised concerns that great apes, who share 98% of their DNA with humans, are also susceptible, but no cases have been documented yet.
There’s some evidence that Covid-19 infects some animals but not others. In a non-peer-reviewed study posted to the open-source journal bioRxiv on March 31, researchers from the Harbin Veterinary Research Institute in China pointed to the susceptibility of cats. “We found that SARS-CoV-2 replicates poorly in dogs, pigs, chickens, and ducks, but efficiently in ferrets and cats,” they wrote. “Surveillance for SARS-CoV-2 in cats should be considered as an adjunct to elimination of COVID-19 in humans.”
Since the study was based on experiments where animals were deliberately infected with SARS-CoV-2 and then tested for the amount of virus in their bodies, cat owners should take the findings with a grain of salt. In an interview with Nature last week, Linda Saif, a virologist at Ohio State University in Wooster, pointed out that the study wasn’t representative of a real-life interaction between animals and humans, so it remains unclear whether pets can pick up the virus elsewhere then spread it to their owners.
What is becoming clear, however, is that owners can pass the virus to their animals. For now, both the CDC and the American Veterinary Medical Association agree that animal owners with Covid-19 should avoid touching their pets and practice frequent hand-washing.
Given the outcry about the shortage of tests for humans, Bronx Zoo officials have clarified that the Covid-19 test used on Nadia the tiger was different from the one used on people and carried out in a veterinary school.
For now, much about the relationship between humans, animals, and Covid-19 remains unclear. Out of an abundance of caution, the United Nations’ biodiversity chief, Elizabeth Maruma Mrema, called for a global ban of wildlife markets, like the one in Wuhan where the outbreak is thought to have started. In an interview with the Guardian today, she warned: “The message we are getting is if we don’t take care of nature, it will take care of us.”