The first two dogs reported to have coronavirus probably caught the infection from their owners, say researchers who studied the animals and members of the infected households in Hong Kong. An analysis of viral genetic sequences from the dogs showed them to be identical to those in the infected people.
Researchers suspected that the infection had been passed from the owners to the dogs, and the direct genomic link strongly supports that, says Malik Peiris, a virologist at the University of Hong Kong who led the study, which is published today in Nature1.
The study showed no evidence that dogs can pass the infection to other dogs or people, but it is impossible to be certain in which direction the virus traveled “so we have to keep an open mind”, says Peiris.
Although the analysis confirms that people with COVID-19 can infect dogs, the probability of this happening is low, says Arjan Stegeman, a veterinary epidemiologist at Utrecht University in the Netherlands. In the study only 2 of the 15 dogs who lived with infected people caught the disease.
But other scientists say the possibility that pets might spread the virus between each other, and to people, needs to be properly investigated as part of managing future outbreaks.
Since the infections in the two canines in Hong Kong — a Pomeranian and a German shepherd — were reported, other pets have tested positive for the SARS-CoV-2 virus, including a cat in Hong Kong and another two in New York state. Four tigers and three lions at New York City’s Bronx Zoo also tested positive. Studies in cats have found that they can pass the virus to other felines without showing symptoms.
The Hong Kong study detected viral RNA and antibodies in both dogs, and live virus in one of them. Neither dog became noticeably sick.
The findings support the results of an April study, in which researchers in China deliberately infected dogs with SARS-CoV-2, says Thomas Mettenleiter, a virologist who heads the Federal Research Institute for Animal Health in Riems, Germany. Dog owners who test positive for the coronavirus should be cautious when handling their pets, he says.
The American Veterinary Medical Association recommends that people who have COVID-19 wear a mask when caring for their pets. It says sick people should also avoid petting, hugging or sharing food with animals, and should wash their hands before and after contact with them.
Role of animals
Beyond protecting pets from the virus, there is an urgent need to test more animals that are in close contact with people, including working animals and livestock, to understand whether they have a role in spreading the virus, says Jürgen Richt, a veterinary virologist at Kansas State University in Manhattan. To do this, specialist diagnostic kits for testing animals will be required, he says.
Richt would also like to see research into whether pets become sick or experience particular symptoms. A common COVID-19 symptom in people is loss of smell. If dogs experience similar symptoms, Richt says this might affect working detector dogs that sniff out drugs, explosives and other illicit items.
Stegeman plans to test cats living with people who have had COVID-19. Understanding the role of domestic and stray cats in the chain of transmission is increasingly important as infection rates between people fall, he says.
Although the Hong Kong study found no evidence of dogs infecting people, Peiris says, their possible role — and that of cats — should be considered in attempts to understand how the virus passed to people in the first instance. Researchers think that SARS-CoV-2 probably originated in bats and passed to people through an intermediate animal, which remains unknown.
A leading theory suggests that the intermediate species came into contact with people in a wild-animal market in Wuhan, China. Dogs, cats and other mammals are sold for meat in such markets, and stray cats and dogs roam around them freely, says Peiris. “The virus seems to have a fairly broad host range. Dogs, cats and other closely related mammalian species could be susceptible and form a bridge between bats and humans,” he says.
But researchers also worry that reports of infected cats and dogs might lead people to abandon their pets. There were news reports of people deserting their pets during the outbreak in Wuhan, where the outbreak originated. “The danger we are facing is that people get nervous when they hear that companion animals could be virus carriers, and decide to get rid of them,” says Richt.