Microbiologists and infectious disease experts in Hong Kong are running tests on the serum of a Pomeranian after it was found to have a low level of infection with the Covid-19 virus.

It was likely the dog was infected by a human at home and it has been the first case in the world that a dog was infected with the Covid-19 virus, Thomas Sit Hon-chung, Assistant Director (Inspection & Quarantine) at the Agriculture, Fisheries and Conservation Department (AFCD), said in a media briefing on Thursday.

The dog has been under quarantine at the animal keeping facility at the Hong Kong Port of Hong Kong-Zhuhai-Macao Bridge from February 26 after its owner, a 60-year-old woman surnamed Chow, was identified as the 85th infected person in the city a day earlier.

The woman, who lived at Block 4, Swiss Towers, at 113 Tai Hang Road, Tai Hang, was said to be a wealthy businesswoman and a member of the Hong Kong Jockey Club. Her Filipino domestic worker and elder brother and his wife were also infected with the coronavirus.

Read: More cases in Hong Kong from two infection chains

The AFCD first collected samples from the dog for tests on February 26, and detected low levels of the Covid-19 virus from its nasal and oral cavity samples on February 27. The department repeated the test on February 28 and March 2, and the dog’s nasal and oral cavity samples, and nasal samples, respectively, tested “weak positive” for the virus.

Experts from the School of Public Health at 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 the dog has a low-level of infection and it is likely to be a case of human-to-animal transmission.

The dog, which has not shown any signs of illness related to Covid-19, was not only “contaminated” but “infected” as its nasal samples had repeatedly tested positive for the coronavirus for six days, Sit said.

“The coronavirus could not have stayed on the mouth and nose of the dog for many days if it was not coming out from its body,” Sit said.

Ho Pak-leung, head of the University of Hong Kong’s Centre for Infection, said Thursday that as Covid-19 can be transmitted between humans, it is likely it can be transmitted from humans to other mammals. However, Ho said there has not been any evidence showing that dog-to-human or cat-to-human transmission is possible.

“People should stay calm. In the 2003 SARS outbreak, samples from eight cats and one dog tested positive, but these cases did not result in any outbreak among animals at that time,” Ho said.

On Tuesday, the dog’s blood samples were taken for an antibody test, which will take five to seven days to complete and show how the animal’s body reacted to the virus. Microbiologists have already finished 80% of the genome sequence process for the dog’s virus and will compare it with that of the coronavirus found in humans to figure out whether genetic mutation had happened, Sit said.

Scientists will also run tests on the dog’s virus on animal cells, particularly respiratory tract cells. There is no registered drug that can cure the infected dog, but hopefully it has already generated some antibodies to fight the virus, he said.

There has not been any information or cases in the world to prove the Covid-19 virus can be transmitted from dog to human, he added. The dog will be returned to its owner only if its samples show negative results in two virus tests.

The Hong Kong government has reported the case to the World Organisation for Animal Health.

The AFCD reminded pet owners to adopt good hygiene practices, including handwashing before and after being around or handling animals, their food, or supplies, as well as avoiding kissing them, and to maintain a clean and hygienic household environment. It said dogs are not required to put on masks as they have to use their tongues to control their body temperature.

However, the AFCD said pet owners need not be overly concerned and under no circumstances should they abandon their pets.

The Hong Kong branch of the Society for the Prevention of Cruelty to Animals also called on pet owners not to dispose of their pets as there has not been any evidence showing that pet-to-human transmission is possible.

It said the infected dog has so far remained healthy in the quarantine facility. It added that the public should understand that “being infected” is different from being “contagious.”

It also said pet owners who feel ill should stop having close contact with pets.