Illustration by Tamara Rees
The refrain when it comes to the novel coronavirus and pets is that there is no evidence that companion animals can spread COVID-19. That remains true, but news out of Hong Kong today suggests the converse may not be true: People, it turns out, apparently can transmit the virus that causes COVID-19 to their dogs.
Hong Kong's Agriculture, Fisheries and Conservation Department (AFCD) reported that three "weak positive" test results over five days on a dog in quarantine indicate "a low level of infection with the virus."
The pet was placed in quarantine and tested after its owner became ill with the novel coronavirus, which first surfaced in December in mainland China and has since spread to more than 80 countries and jurisdictions. A tally maintained by the Center for Systems Science and Engineering at Johns Hopkins University shows 95,124 human cases worldwide as of 7 pm EST. Of those, 51,171 patients have recovered and 3,254 have died.
Despite the indication of infection, the dog shows no clinical signs of disease related to the COVID-19 virus, according to the press release. The virus is called SARS-CoV-2. In people, illness from the virus generally involves fever, cough, shortness of breath and fatigue. In a small subset of patients, the disease is life-threatening. Some infected people are believed to have no symptoms at all.
A second dog being quarantined in a separate room of the same facility in Hong Kong tested negative for the virus, according to the government statement. The AFCD "strongly" advises that pet mammals from households with confirmed human cases of COVID-19, or from households of people in close contact with COVID-19 patients, be put in quarantine at AFCD facilities.
The fact that the infected dog doesn't appear ill from the virus doesn't mean dogs aren't susceptible, according to Dr. J. Scott Weese, an expert in infectious diseases and a professor at the University of Guelph's Ontario Veterinary College.
"People can get infected without getting sick, so it's too early to say one way or the other what this result means in the broader canine picture," Weese wrote in a blog post today.
Hong Kong authorities initially raised the possibility that the dog's nose and mouth had merely become contaminated with the virus from its environment. But the repeated positive test results disproved that, the government statement indicates.
"Experts from the School of Public Health of The University of Hong Kong, the College of Veterinary Medicine and Life Sciences of the City University of Hong Kong and the World Organisation for Animal Health (OIE) have been consulted, and unanimously agreed that these results suggest that the dog has a low level of infection and it is likely to be a case of human-to-animal transmission," the statement reads.
The fact that the dog does not appear to be sick from the virus suggests that "replication of the virus in the dog has not been sufficient to cause the dog to become ill," Dr. Gail Golab, chief veterinary officer at the American Veterinary Medical Association, said in an emailed statement.
She added, "Important to note is that the U.S. Centers for Disease Control and Prevention, the World Health Organization, and the Hong Kong AFCD continue to share that there is no evidence that companion animals can spread COVID-19."
Experience with the virus so far suggests that dogs "are not important epidemiologically in the spread of COVID-19," according to Dr. Melissa Kennedy, a virologist and associate professor at the University of Tennessee College of Veterinary Medicine.
That's because transmissions to date primarily have been traced to contact between humans rather than with pets. "Plus, if dogs were an important vector, I would have expected this to have occurred in [mainland] China, which has given no indication that this is the case, i.e., I would have expected multiple cases by now," Kennedy said by email.
All the same, people who have been exposed to or infected by the virus should stay away from animals, experts advise. "Preventing exposure of animals at least helps them from being fomites," Weese said by email, referring to the possible spread of the virus via animals' fur, in the same manner that contaminated doorknobs and other objects can serve as vehicles for disease transmission.
This story has been changed from the original to clarify the distinction between the disease COVID-19 and the virus that causes it.
Update: The Hong Kong government reported on March 12 that a blood test on the pet dog came back negative for antibodies to the COVID-19 virus. The statement continues: "The negative serological test result does not suggest that the dog has not been infected with the virus. It is known in some asymptomatic or mild cases of human infections with other types of coronavirus that antibodies may not always develop. It is also not uncommon in the earlier stages of infections to have a negative result, as it often takes 14 days or more for measurable levels of antibodies to be detected. Another blood sample will be taken later for further testing." The dog continues to show no signs of illness related to COVID-19. The full statement is posted here.
March 26 update: The Hong Kong government announced today that subsequent testing of blood from the dog was positive for antibodies to the virus that causes COVID-19. The statement called the result proof that the dog had been infected. However, it underscored that cases of infection in dogs appear to be infrequent. As of March 25, the government had conducted tests on 17 dogs and eight cats from households with confirmed COVID-19 cases or persons in close contact with confirmed patients, and only two dogs had tested positive, according to the statement.