The first dog in the U.S. presumed to have COVID-19 may not have been infected with the virus after all, according to test results recently confirmed by the U.S. Department of Agriculture.
The USDA tests completed last week could not confirm signs of infection from the virus that causes COVID-19 or antibodies in his system that would indicate a prior infection in Winston, a pug in North Carolina.
"The National Veterinary Services Laboratories (NVSL) conducted confirmatory testing but were unable to verify infection in the dog. No virus was isolated and there was no evidence of an immune response using the available test," agency spokesperson Lyndsay Cole said in a statement.
Cole and researchers from Duke University say they suspect original positive result was a result of virus in the household, where members of the family were positive for COVID-19, contaminating the sample taken from the dog. Winston and other pets in the home were originally tested because the family is participating in a study to better understand the virus.
In late April a researcher from the study announced that Winston tested positive for the virus, which would have been the first known case in the U.S. of the virus in a dog. Elizabeth Petzold, program manager on the Duke University study that conducted the original test, said that to get more reliable results going forward researchers plan to rely on antibody tests from blood samples rather than swabs to test for the virus.
"Serology testing showed none of the 3 animals in this home had generated an antibody response detectable by the test used, which likely means they were never systemically infected. It seems more likely that the virus was picked up by the animals via environmental contamination from the surfaces in the home," she said in a statement.
"Going forward, we will begin collecting a small blood sample on all animals in the study to see if we can detect any animals with antibodies. We hope to learn more as the study progresses.”
At the time the positive result was announced by Duke it had not been confirmed by the USDA's National Veterinary Services Laboratory, which is considered the official source of confirmed results for COVID-19 tests on animals, in part because it is the entity that officially notifies the World Organisation for Animal Health of any positive cases of infectious disease in animals in the U.S. When Duke University first reported the case, the USDA said it had not yet received a sample and that while it considered it a presumptive positive, it could not confirm the results.
Since then USDA had to go back to collect new samples from the dog and process the tests, which were completed last week.
The new results were first reported by The Canine Review.
Animals can transmit viruses to humans in what are known as zoonotic diseases but throughout the pandemic veterinarians and the CDC have said there is no evidence pets can easily transmit COVID-19 to humans. But experts acknowledge little is known about this virus and recommended isolating family pets from those sick with COVID-19.
The American Veterinary Medical Association says pet owners should practice good hygiene when interacting and picking up after pets and should not let pets interact with people or animals outside the household, including keeping cats indoors and avoiding dog parks or large public gatherings with pets.
"The fact that this dog doesn’t appear to have been infected with SARS-CoV-2 doesn’t change the AVMA’s recommendations regarding pets," said spokesman Michael San Filippo.
"There have been a handful of dogs and cats that have tested positive, so we know the potential is there for infection, even if it’s highly unlikely. But at this point in time, there is no evidence to suggest that pets that may be incidentally infected by humans play a substantive role in the spread of COVID-19."
Filippo added that there is no reason to remove pets from homes even when family members are infected unless they are unable to care for the animal. Still, extra precautions should be taken to restrict contact between people with COVID-19 and pets.
Authorities in Hong Kong reported a "weak positive" for a dog in March after it's owner tested positive for the virus.
The USDA has also confirmed that two domestic cats tested positive for COVID-19. Eight big cats at the Bronx Zoo also tested positive and are believed to have contracted the virus from a zoo staff member who was carrying the virus but exhibited no symptoms.
AVMA and USDA say they don't think widespread testing is necessary for animals at this point but if pet owners are concerned or think their animal may have been exposed to COVID-19 to contact their veterinarian.