A sick cat at the San Diego Humane Society. Dogs and cats were found harboring variant B.1.1.7 SARS-CoV-2.
ARIANA DREHSLER / AFP via Getty Images
By David Grimm
ScienceCOVID-19 reports are supported by the Heising-Simons Foundation.
The variants of SARS-CoV-2 that continue to emerge are not just a human problem. Two reports released this week found the first evidence that dogs and cats could be infected with B.1.1.7, a recent variant of the pandemic coronavirus that is more easily transmitted among people and also appears to be more lethal in them. The findings mark the first time that one of several major variants of concern has been seen outside of humans.
B.1.1.7 was first identified in the UK and is where some of the pets infected with variants were found. UK animals have suffered from myocarditis – an inflammation of cardiac tissue that, in severe cases, can cause heart failure. But the reports offer no proof that the SARS-CoV-2 variant is responsible, nor that it is more transmissible or dangerous in animals. “It’s an interesting hypothesis, but there is no evidence that the virus is causing these problems,” said Scott Weese, a veterinarian at Ontario Veterinary College at the University of Guelph, specializing in emerging infectious diseases.
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Since December 2020, scientists have identified several variants of concern that appear to be more transmissible or are able to prevent some immune response. B.1.351, for example, was first detected in South Africa, and a strain called P.1 was found for the first time in Brazil. Variant B.1.1.7 caught the eye from the start because of its rapid growth in the United Kingdom; it now comprises about 95% of all new infections there.
So far, the impact of these variants on pets is unclear. Although there are already more than 120 million cases of COVID-19 worldwide, only a handful of pets tested positive for the original SARS-CoV-2 – probably because no one is testing them. Infected pets appear to have symptoms ranging from moderate to nonexistent, and infectious disease experts say pets are likely to play little, if any, role in spreading the coronavirus to people.
The new variants could change that equation, says Eric Leroy, a virologist at France’s National Research Institute for Sustainable Development, specializing in zoonotic diseases. In one of the new studies, he and his colleagues looked at pets admitted to the cardiology unit at the Ralph Veterinary Referral Center outside London. The hospital noted a sharp increase in the number of dogs and cats with myocarditis: from December 2020 to February, the incidence of the disease jumped from 1.4% to 12.8%.
This coincided with an increase in variant B.1.1.7 in the United Kingdom. Therefore, the team analyzed 11 pets: eight cats and three dogs. None of the animals had a previous history of heart disease, but all had symptoms ranging from lethargy and loss of appetite to rapid breathing and fainting. Laboratory tests revealed cardiac abnormalities, including irregular heartbeat and fluid in the lungs, all symptoms seen in human cases of COVID-19.
Seven of the animals did polymerase chain reaction tests and three tested positive for SARS-CoV-2 – all with variant B.1.1.7, the team reported yesterday on the prepress server bioRxiv. Tests for SARS-CoV-2 antibodies in four of the other animals detected evidence that two of them had been infected with the virus. Earlier this week, researchers at Texas A&M University detected variant B.1.1.7 in a cat and dog from the same house in Brazos County.
The Texas owner was diagnosed with COVID-19, and the owners of five of the UK’s 11 pets tested positive for SARS-CoV-2 – all before their animals developed symptoms. Texas pets showed no symptoms at the time they were tested, although the two started sneezing several weeks later. All the animals in the US and the UK have recovered since then, although one of the cats in the UK has relapsed and had to be euthanized.
Leroy says it is not clear whether B.1.1.7 is more transmissible than the original strain between humans and animals, or vice versa. It is “impossible to say” that pets infected with B.1.1.7 may play a more serious role in the pandemic, he adds, but “this hypothesis has to be seriously raised”.
Shelley Rankin, a microbiologist at the School of Veterinary Medicine at the University of Pennsylvania, points out that the researchers showed only a correlation between B.1.1.7 infection and myocarditis, and that they did not rule out other causes for the disease. “There is no evidence that pets were sick from the virus,” she says.
Weese agrees that neither the Texas nor the UK findings should sound any alarms about pets putting their owners in danger. “The risk of being a source of infection remains very low,” he says. “If my dog is with him, he probably inherited it from me. And I am much more likely to infect my family and neighbors before him. “
Still, he says scientists and veterinarians should conduct studies on the role, if any, of SARS-CoV-2 and its variants in myocarditis among pets. There is evidence that the virus can cause disease in people, Weese notes, so it is worth exploring in pets. “It may be real,” he says, “but there is no reason for people to freak out now.”