There are still many unanswered questions about the novel coronavirus, but this week, new and surprising information about the transmission of the virus was revealed: A tiger at the Bronx Zoo tested positive — and health officials say she caught it from a zoo employee who had COVID-19, but was asymptomatic. The big cat is expected to recover, but its diagnosis worried many pet owners. Could their feline friends get the virus, too?
Researchers in China say they've determined that domestic cats are susceptible to airborne infection with the coronavirus. In a new study published in Science, scientists from Harbin Veterinary Research Institute intentionally exposed groups of cats, dogs, ferrets, pigs, chickens and ducks to the virus, and found some animals are more susceptible than others.
Fortunately for dogs, the researchers found that man's best friend has a low susceptibility to the virus. Livestock including pigs, chickens, and ducks also did not appear to be significantly affected by it.
However, both ferrets and cats do appear to be susceptible to infection, the study finds. To determine this, researchers inserted the virus, SARS-CoV-2, into the noses of five domestic cats. Three of the infected cats were put in cages next to uninfected ones. The researchers later found the virus in one of the exposed cats, suggesting it contracted the virus from droplets in the breath of the infected cats nearby.
The four cats that had coronavirus also developed antibodies against the virus. The researchers say knowledge of how the virus replicates in animals could be helpful in efforts to develop treatments for COVID-19 in humans. However, the study also raises many other questions.
For one thing, this experimental study might not mimic the way germs are spread in real life, Dr. Ann Hohenhaus, an internal medicine and small animal veterinarian at New York City's Animal Medical Center, told CBS News. "They took a known amount of virus and squirted it up the nose of the animals they were testing," she explained.
"When you do research, you got to start somewhere, so that was a big dose of the virus right up the nose. And I don't think there's anybody who thinks that mimics the situation out there of you and your pet in an apartment in New York City," Hohenhaus said, adding the study was an important step in the research of coronavirus and animals.
The veterinarian said she has read countless studies that looked at coronavirus in various animals, and much of the research has not surprised her.
"Ferrets have been used for a long time to study upper respiratory disease in people and to help study disease and make vaccines. So, there's something to the ferret respiratory tract that makes the susceptible to our diseases," she said. "If you look at the genetics of the cat receptor... cats and people are almost identical."
"So, knowing that, you would say, 'Oh that virus should be able to get into a cat's cell,'" Hohenhaus said. "Dogs are only about 70% the same. So that piece of information explains why dogs are less susceptible because their receptor is not as friendly to letting the virus in."
Still, she said veterinarians, the CDC and U.S. Department of Agriculture are giving pet owners the same advice they've continued to give during this pandemic. "Wash your hands before you touch your pet, wash your hands after you touch your pet. If you're sick, wear a mask... you should not take care of your pet and find a surrogate to take care of your pet so that you can quarantine yourself away from everyone in the family, which includes all pets," Hohenhaus said.
While both domestic cats and big cats may be able to catch the virus, there's so far little evidence of risk to people's pets — and no sign of anyone actually catching the virus from a cat or dog. The domestic cats in the Harbin Veterinary Research Institute did not show any symptoms once infected with coronavirus.
In the Bronx Zoo case, a tiger named Nadia, which tested positive for the virus, her sister Azul, two Amur tigers and three African lions all developed a dry cough and decrease in appetite. They are all expected to recover, the zoo said.
A Malayan tiger at the Bronx Zoo in New York tested positive for the coronavirus. Julie Larsen Maher / Bronx Zoo
The USDA said the Bronx Zoo's tiger is the "first case of its kind" and "further studies are needed to understand if and how different animals could be affected by COVID-19."
"There is no evidence that animals play a role in the transmission of COVID-19 to people," the USDA said in a press release, although early cases may have been linked to a food market where wild species were sold in Wuhan, China. In addition, there is "no evidence that any person has been infected with COVID-19 in the U.S. by animals, including by pet dogs or cats."
According to the U.S. Centers for Disease Control and Prevention, a small number of pets outside the United States have been reported to be infected with the virus after close contact with people with COVID-19 — but not the other way around. "We do not have evidence that companion animals, including pets, can spread COVID-19 to people or that they might be a source of infection in the United States," the CDC says.
Hohenhaus offered more evidence to reassure pet owners who may still be worried.
"Here's what I think has been underreported and should make people happy," she said. "IDEXX, an international veterinary laboratory company, has developed a screen test for animals for COVID-19 and veterinarians from all over the world send samples from animals with respiratory infections to IDEXX, trying to identify what's wrong." Thousands of animals have been tested and not one has tested positive for the coronavirus, the company said in a press release.
"These new test results align with the current expert understanding that COVID-19 is primarily transmitted person-to-person and supports the recommendation against testing pets for the COVID-19 virus," the company said. "For dogs or cats presenting with respiratory signs, the recommendation is to contact a veterinarian to test for more common respiratory pathogens."