The Bronx Zoo, which opened in 1899, can boast of many milestones during its long and illustrious history. This past weekend, the zoo became the site of another first, when one of its tigers became the first animal to test positive for COVID-19 in the United States.
“This is the first instance of a tiger being infected with COVID-19,” noted the United States Department of Agriculture’s (USDA) statement on the confirmation of COVID-19 in the tiger.
Samples from the tiger were tested after “several lions and tigers at the zoo showed symptoms of respiratory illness.” The first tiger began showing signs of sickness on March 27. The zoo tested only one tiger because, they explained, the collection of samples in big cats requires general anesthesia and the veterinarian “felt it was in the best interest of the animals to limit the potential risks of general anesthesia” to one tiger.
The infection was confirmed by the USDA National Veterinary Services Laboratories. The zoo clarified—by tweeting a statement on Sunday evening from Paul Calle, DVM, Bronx Zoo chief veterinarian—that the testing used for the tiger uses a separate process than human testing. Calle noted that, “The COVID-19 testing that was performed on our Malayan tiger Nadia was performed in a veterinary school laboratory and is not the same test as is used for people.” Calle continued, “You cannot send human samples to the veterinary laboratory, and you cannot send animal tests to the human laboratories, so there is no competition for testing between these very different situations.”
The good news is that all of the large cats at the zoo are expected to recover and there is no evidence that other animals in other areas of the zoo are showing symptoms. Therefore, the zoo will not be performing routine testing.
“This shows us that when a new virus suddenly appears, you just never know how it will behave,” noted Steve Higgs, PhD, associate vice president for research and director of the biosecurity research institute (BRI) at Kansas State University and the editor-in-chief of Vector-Borne & Zoonotic Diseases. “Who knows how the tiger was infected,” added Higgs. Officials think that the large cats were exposed by a zookeeper, as the zoo has been closed to the public since mid-March. Asked about that possibility, Higgs answered that he is not sure how close zookeepers get to tigers… but knows that it is “closer than he would want to get—for sure!”
Beyond the zoo
Several research teams in China have been looking into which animals SARS-CoV-2 can infect. One paper, published by a team from the Huazhong Agricultural University in Wuhan, China, surveyed serum samples taken from cats in Wuhan, China. The study, entitled, “SARS-CoV-2 neutralizing serum antibodies in cats: a serological investigation,” was published in the preprint server bioRxiv.
The team analyzed 102 samples after the COVID-19 outbreak in Wuhan, and 39 prior to the outbreak. Out of the 102, 15 (14.7%) cat sera collected after the outbreak tested positive for the presence of antibodies against the receptor-binding domain (RBD) of SARS-CoV-2 by indirect enzyme linked immunosorbent assay (ELISA).
Among the positive samples, 11 had SARS-CoV-2 neutralizing antibodies with a high titer. Interestingly, the three cats owned by COVID-19 patients had the highest neutralization titer. In addition, there was no serological cross-reactivity detected between the SARS-CoV-2 and type I or II feline infectious peritonitis virus (FIPV).
These findings are the first to suggest that SARS-CoV-2 infected the cat population in Wuhan during the outbreak, and to demonstrate that animals produce specific neutralizing antibodies against SARS-CoV-2 under natural conditions.
“To date, very few domestic animals/pets have tested positive,” Higgs asserted. But, he added, “These are experiments that definitely need to be done.”
Another study, from the Harbin Veterinary Research Institute in Harbin, China, investigated the susceptibility of ferrets, cats, and other animals that are typically in close contact with humans to SARS-CoV-2. The team also looked at the replication dynamics of the virus in these animals.
The paper, which also appeared as a bioRxiv preprint, is titled “Susceptibility of ferrets, cats, dogs, and different domestic animals to SARS-coronavirus-2.”
The researchers found that ferrets and cats are highly susceptible to SARS-CoV-2 and that the virus replicates efficiently in both animals. They suggest that the efficient replication of SARS-CoV-2 in ferrets makes them a candidate animal model for evaluating antiviral drugs or vaccine candidates against COVID-19.
Not only did the study find that the cats in this study were “highly susceptible to SARS-CoV-2,” they also found that the virus transmits in cats via respiratory droplets. Because of the efficient replication and transmission to naïve cats, the authors noted that, “surveillance for SARS-CoV-2 in cats should be considered as an adjunct to the elimination of COVID-19 in humans.”
Some good news came out of the study, when they looked at other animals. Dogs were found to have low susceptibility, and livestock including pigs, chickens, and ducks were not susceptible to the virus.
Can your cat give you COVID-19?
The Centers for Disease Control states that they “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.”
Although there have not been reports of pets becoming sick with COVID-19 in the United States, it is still recommended that people sick with COVID-19 limit contact with animals until more information is known about the virus. To protect your pets, the CDC states that anyone sick with COVID-19 should “restrict contact with pets and other animals” out of an abundance of caution—just as they would with other people. And, if a sick person must care for a pet or be around animals, they should follow the same advice that has been the cornerstone of the public safety message since the beginning of the outbreak—including washing their hands before and after the interaction.