A second dog in Hong Kong has an infection of the novel coronavirus that causes COVID-19, likely contracted from its infected owner, authorities there announced Thursday.

However, there's no evidence to date that pets develop the clinical disease COVID-19 or transmit the virus to people, and experts question the implications of the reported positive tests in dogs.

The new case in Hong Kong involves a young German shepherd from a residential neighborhood who "repeatedly" tested positive for SARS-CoV-2, the coronavirus responsible for COVID-19, according to a press release from Hong Kong's Agriculture, Fisheries and Conservation Department. A second dog in the same household, a mixed-breed, has not tested positive, the press release states. Both pets are in quarantine.

In people, COVID-19 is a respiratory illness that can cause anything from mild symptoms — principally fever, cough and fatigue — to life-threatening pneumonia.

Worldwide COVID-19 cases have surpassed 255,000, and more than 10,000 people have died of the disease, according to the Center for Systems Science and Engineering at Johns Hopkins University, which keeps a running tab on positive cases.

In Hong Kong, neither dog has shown any clinical signs related to the virus, despite the test results indicating infection, according to government authorities. They said the same of the world's first canine to test positive for SARS-CoV-2 — a 17-year-old Pomeranian that died Monday, three days after going home, according to a report in the South China Morning Post. 

In a statement, the World Small Animal Veterinary Association said the dog had "significant unrelated health problems including cardiac and renal issues and is believed to have passed away from these and old age, possibly exacerbated by the stress of quarantine away from familiar surroundings." 

Moreover, there's no evidence that COVID-19 can be contracted from pets, WSAVA President Dr. Shane Ryan said: "While there is still much we don't know about COVID-19, we do know that the pomeranian dog did not die from the virus, and the second dog is also showing no signs, either of the disease or of being able to transmit it to other pets or people."

In an interview with the VIN News Service, Dr. Mark Rishniw explained that positive tests of viral genetic material in dogs do not mean they can get sick from or help spread the novel coronavirus. 

"Chances are that dogs can be infected, but there's no evidence that the virus can replicate successfully in dogs," said Rishniw, director of clinical research for the Veterinary Information Network, an online community for the profession and parent of VIN News.

"Until they actually isolate the virus out of the dogs and not just RNA [the virus's genetic material], then there's no evidence that the dog is transmitting the virus,” he said. "How the dog actually deals with a virus that it has picked up, what type of immune response it produces against the virus, and whether or not the virus can actually replicate in the dog and be excreted as a formed, infective virus — that remains to be determined."

Rishniw, an adjunct professor at Cornell University College of Veterinary Medicine, added by email: "The risk for a pet becoming infected is quite small given the number of confirmed cases in dogs, compared to the number of infected people, many of whom likely have dogs or cats. However, little testing of pets of infected owners is going on at present, so the true transmission rate from infected person to pet is unknown.

He continued: "Now, if someone can isolate a complete virus from the saliva of a dog or cat, then I might change my tune. Viruses are species-specific, for the most part, for a reason. And this one probably came from a bat."

The possibility that a bat was the original host reservoir of SARS-CoV-2 is the topic of a study published Tuesday in the journal Nature Medicine. "Although no animal coronavirus has been identified that is sufficiently similar to have served as the direct progenitor of SARS-CoV-2, the diversity of coronaviruses in bats and other species is massively undersampled," the authors write.

Testing pet populations

While researchers try to trace the origins of the virus and how best to fight it, Antech Diagnostics and Idexx Laboratories, two separate large veterinary reference laboratory chains, say they have been watching for SARS-CoV-2 through RT-PCR tests of specimens from pets.

PCR stands for polymerase chain reaction, a molecular-biology technique in wide use that enables scientists to quickly amplify a small sample of genetic material in order to study it. RT stands for "reverse transcriptase," the process of using an enzyme to generate complementary DNA from an RNA template.

The test being deployed by veterinary diagnostic laboratories is "essentially the same type of test the CDC [U.S. Centers for Disease Control and Prevention] uses," Rishniw explained.

The labs' surveillance programs involve testing samples from dogs and cats that are submitted for respiratory PCR analysis. To date, they have not detected SARS-CoV-2, the companies reported in recent press releases. 

However, the labs have not tested any animals with known contact with an infected person, said Dr. J. Scott Weese, a professor in the pathobiology department at the University of Guelph in Ontario and an expert on zoonotic diseases. "So, the lack of positive results means nothing (except the test doesn't cross-react, which is good),” he said by email.

Weese discourages the use of such tests, which are being marketed to veterinarians and pet owners. "We only want testing done through an organized surveillance program," he said. "We don't want people taking animals to vets for testing. ... Since there's a reasonable chance that they are infected (the reason to test), we want them confined to the household. 

"Also," Weese added, "sampling involves some risk to vets if the animal is truly infected, and vets are not typically well equipped or trained for protection against respiratory pathogens." 

Antech, operated by Mars Petcare, said in its press release that it would share any discovery of SARS-CoV-2 with health authorities.

"We are actively monitoring the situation and communicating regularly with our academic partners, veterinary customers, veterinary health organizations and government agencies internationally," Dr. Jennifer Ogeer, vice president of Antech medical affairs and commercial marketing, said in a news release Thursday.

Idexx President Jay Mazelsky, in a March 13 news release, said: "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. For dogs or cats presenting with respiratory signs, the recommendation is to contact a veterinarian to test for more common respiratory pathogens." 

Asked whether their tests might be used to help detect SARS-CoV-2 in humans, Idexx officials said the company's laboratories are designed for veterinary diagnostics only. In a statement to VIN News, the company said: "The IDEXX COVID-19 test was developed specifically for use in animals and was carefully designed to avoid cross reactivity with other veterinary-specific coronavirus strains that infect pets. ... Given our focus on and expertise in veterinary diagnostics, our laboratories are not approved for handling human specimens."

March 26 update: The Hong Kong government announced today that subsequent testing of blood drawn on March 3 from the first dog, the Pomeranian, 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.