With the rapid global spread of SARS-CoV-2, one concern has been whether the new coronavirus can spread between people and their pets. There have been isolated reports of infections in domestic cats and dogs, as well as a tiger and a lion at a New York zoo. The tiger and lion had been kept in a group that had developed respiratory signs over the course of a week and later recovered following supportive treatment. The infected animals had all been in close contact with infected people, raising questions about the transmission dynamics of the virus between humans and other animals. Early research has focussed on finding out how susceptible different animals are to the new coronavirus, to better inform control measures and to protect the welfare of humans and their pets.
Can my cat get COVID-19?
Researchers have used two different approaches to study whether SARS-CoV-2 can infect cats.
In the first study, researchers evaluated the prevalence of SARS-CoV-2 in cats during the COVID-19 outbreak in Wuhan. Domestic, hospitalised, and stray cats were all tested for prior exposure to the new coronavirus using an antibody-based test. Cats exposed to the new coronavirus produced specific antibodies against the virus that were measured using an antibody-based test. When just over 100 blood samples from cats were tested, 14.7% of the cats tested positive, indicating that the cats had become infected with the new coronavirus. This finding suggested that SARS-CoV-2 could spread directly from people to cats, as three cats that were owned by COVID-19 patients gave the most strongly positive test results. Also, samples collected from cats before the COVID-19 outbreak all tested negative for antibodies. This tells us that cats were not infected with closely related coronaviruses before the emergence of SARS-CoV-2 in humans.
The second study involved experimentally infecting a small number of cats in a controlled laboratory environment. Virus genetic material was detected in samples taken from the upper airways, small intestine and faeces of the infected cats. It was also possible to isolate infectious virus from upper airway samples, providing further evidence that cats are susceptible to SARS-CoV-2 infection. The study also suggested that it might be possible for the virus to be transmitted between cats without direct contact, although these data have not been confirmed, and it remains unclear whether infection was transmitted by respiratory droplets or contaminated faeces. These experimental findings are suggestive, not definitive, because the study was limited to a small number of animals, and used high doses of virus that did not necessarily reproduce the amount of virus, nor routes of viral spread, that occur during day-to-day interactions between pets and their owners.
Together, these studies demonstrate that cats are susceptible to SARS-CoV-2 infection and are most likely become infected from close interactions with infected people. There are reports that some animals develop illness with symptoms of respiratory distress and diarrhoea that has cleared up. Cat owners with COVID-19 can prevent their pets from getting infected with coronavirus by maintaining good hygiene, including hand washing, while handling and interacting with their animals.
Can SARS-CoV-2 infect other animals?
There have been a few isolated reports of SARS-CoV-2 infection in dogs, but no systematic studies. The first confirmed case was that of a 17-year old Pomeranian dog in Hong Kong. Swabs for testing were collected from the oral and nasal cavities of the dog and a sample was collected from its owner. Genome sequencing showed that the virus samples taken from both the dog and its owner matched and so it was likely the virus had been transmitted from the owner to the dog. The dog continued to test positive for the virus genome twelve days after it was removed from its household, although it was not possible to isolate infectious virus from the samples. Difficulty in isolating infectious virus from dogs has been reported elsewhere, which might suggest that dogs are not actively shedding virus and are more able to resist infection than cats. Ferrets have also been shown to be susceptible to SARS-CoV-2 infection in the laboratory, developing active infections and signs that would normally be associated with human COVID-19, such as elevated body temperatures, reduced activity and an occasional cough.
To date, SARS-CoV-2 infections have been reported in cats, dogs, hamsters and ferrets, but there is no evidence yet that birds including ducks and chickens are susceptible to SARS-CoV-2 infection. The factors that govern why one animal is susceptible to the new coronavirus while others are more resistant are unknown, but might reveal more about how this virus spreads and causes disease.