A pet dog in Hong Kong has a “low-level” infection of the coronavirus that causes covid-19 in people, in what may be the first known human-to-animal transmission of the novel coronavirus that has sickened more than 90,000 people worldwide.

The case has raised the specter that dogs might be swept into the epidemic, which, even now, public health officials say does not appear to infect or be spread by pets. But experts say much remains unknown about the dog’s infection, and they emphasized the lone case is not yet cause for alarm or reassessments about interactions with pets.

The dog is owned by a person who was hospitalized with covid-19, and it has been quarantined since Feb. 26, according to Hong Kong’s Agriculture, Fisheries and Conservation Department. The department said last week that the dog’s “weak positive” test results, from nasal and oral swabs, might have been the result of “environmental contamination,” not infection. But positive tests since then suggest the dog does have a low-level of infection, the department said Wednesday. The animal has shown no symptoms, and a second dog under quarantine in the same facility has tested negative for the virus, the department said.

“At this point, we can say there’s evidence dogs can get infected, but we have no idea what that means for dogs or people … is it one of a million or is it one of 10? We have no idea,” said J. Scott Weese, a professor at the University of Guelph’s Ontario Veterinary College who studies zoonotic disease. But, he added, “a weak positive would suggest there’s not a lot of virus there.”

President Trump has said warm weather could slow the spread of the novel coronavirus, but experts explain it's too early to know if the virus is seasonal. (The Washington Post)

Weese said he is less concerned about the possibility of dogs becoming widely infected with the novel coronavirus than he is about cats, which, along with ferrets, were shown to be susceptible to infection with the SARS virus in laboratory experiments. A study published in late January in the Journal of Virology, he noted, predicts the virus that causes covid-19 can attach to receptor cells present in cats, pigs, ferrets and some primates — meaning those species might be at greater risk of being infected.

“The big question for me is: Is it exclusively a human virus, or is it predominantly a human virus right now?” Weese said. “What we don’t want to do is get an animal reservoir,” that could spread the virus, he added, such as feral cats. “But that’s probably unlikely.”

That a dog is infected with the virus is not surprising, said Gregory C. Gray, an infectious disease epidemiologist at Duke University. Coronaviruses are “promiscuous” and move between species, he said. The novel coronavirus is believed to have originated in bats and may have passed to humans from pangolins; the SARS coronavirus came from bats via civet cats; and other types of coronaviruses are common among canines.

“Certainly, it raises the hypothesis that perhaps dogs could play a role in the ecology of SARS-CoV-2 transmission to man, but you’d be going way out on a limb to assume that right now,” said Gray, referring to the virus that causes covid-19 in people. “I don’t see any reason to change the social connectivity with our dogs or other dogs or to put any sort of respiratory apparatus on the dogs, like we’ve seen on the Internet.”

Maria Van Kerkhove, an infectious disease epidemiologist serving as technical lead for the World Health Organization’s coronavirus response, said at a news conference Thursday that the dog is an older animal that is “doing well.” The organization and its partners are looking more closely at other pets of covid-19 patients, she said.

Michael Ryan, executive director of the WHO Health Emergencies Program, told reporters that the role of animals is “always a question” with emerging diseases.

“Are animals intimately associated with the spread of this disease? The answer to that is no,” Ryan said. “This dog was a victim, more than others, and we need to establish quite clearly what part animals might play in further transmission.”

The Hong Kong government said it had consulted with local public health and veterinary experts, as well as the World Organization for Animal Health, before concluding the dog was infected. The dog will remain in quarantine until it tests negative, the agriculture department said, adding it “strongly advises” people who have covid-19 or have had close contact with infected people to quarantine any pet mammals.

But there’s no reason to fear pets, the department said.

“Apart from maintaining good hygiene practices, pet owners need not be overly concerned, and under no circumstances should they abandon their pets,” the department said.

Gail Golab, chief veterinary officer with the American Veterinary Medical Association, said in an email that the Hong Kong dog’s lack of symptoms could mean it “has a low level of infection, but that replication of the virus in the dog has not been sufficient to cause the dog to become ill.” Given that, she said, the association’s advice to pet owners remains the same: Focus on hygiene, and if ill, stay home and away from pets — “including petting, snuggling, being kissed or licked, and sharing food."

Humans can transmit pathogens to animals, though this direction — sometimes called “reverse zoonosis” — is less-studied than animal-to-human transmission, Gray said. Chimpanzees in several countries in Africa, for example, have been hard hit by respiratory illnesses that came from humans.

Most important for now is that people who are infected with or have been exposed to covid-19 think about their pets, too, Weese said — because of the unknowns about their vulnerability to infection, and because a pet can host the virus on its fur or skin, just as cash or a doorknob might.

“If I’m self-isolating at home and living in my basement, away from other people, but my cat comes to sit on my lap, and I cough on it and pet it, and it runs upstairs and rubs against my kid and goes outside, then we’ve maybe got a little bit of a problem,” Weese said. “Consider your cat just like your kid.”

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