Bengaluru: A study by researchers from Hong Kong and Australia has established the presence of Covid-19 in dogs, even though it couldn’t conclude how exactly the infection affects them. The study, a preprint that is yet to be peer-reviewed, was uploaded on Nature last week.
As the coronavirus pandemic rages across the world, with a toll of over 3.1 lakh and counting, many researchers have been looking into the impact of the virus among animals, including pets.
Studies so far have suggested that domestic cats can transmit the coronavirus among themselves, and the virus has also been reported jumping from an asymptomatic employee to multiple big cats in a New York zoo.
A global pandemic and two dogs
The new study is based on two pet dogs from Hong Kong who tested positive for Covid-19 after their humans were diagnosed with the virus. It indicates that dogs can get the virus from humans.
The subjects of the study were a 17-year-old neutered male Pomeranian (the average life span of this breed is 12-16 years), and a 2.5-year-old German Shepherd. While the former had a number of underlying illnesses, including a heart condition, hypothyroidism, chronic kidney damage, and pulmonary hypertension, the second was healthy except for the Covid-19 infection. Nasal and oral swabs obtained from both dogs yielded a positive coronavirus diagnosis, while their rectal and faecal samples tested negative.
Both dogs also had antibody responses to the virus, which indicates they weren’t merely carrying it but were actually infected, leading their immune systems to produce antibodies to fight the infection. The animals remained asymptomatic through their entire time in quarantine.
The researchers discovered that the viral genetic sequences from both dogs were identical to those detected in the infected humans they lived with — a suggestion that the virus jumped from the humans to the dogs. This suggests the virus didn’t mutate into a new form within these dogs.
The household with the Covid-positive German Shepherd also had another dog, which tested negative.
Despite these findings, a lot of questions about Covid-19 in animals remains a matter of research, including how the disease manifests in pets and whether they can die of Covid-19.
The older Pomeranian died two days after being released from quarantine, but the researchers suggested this could be because of its numerous health conditions. The dog’s human refused permission for an autopsy.
Previous research has shown that when adult dogs or puppies are purposely exposed to the virus, they do test positive, but do not necessarily infect other canines. This, a Chinese study suggested in April, was because of insufficient viral loads in dogs. The case was different with cats, who have been found to infect other felines with Covid-19.
The findings of such research have implications for understanding any future zoonotic transmissions. The extent of risk for pets is still unclear, and it is not known conclusively whether they can transmit the virus among themselves or back to humans. This study sampled only two dogs, and further studies are necessary to draw conclusive evidence about whether domestic dogs or cats can play a role in spillover events (where a virus jumps from one species to another).