Winston the pug can breathe a sloppy sigh of relief: He is not the first dog in the United States to be infected with the coronavirus.
That was the conclusion of the U.S. Department of Agriculture’s National Veterinary Services Laboratories, which “was unable to verify infection in this dog,” a U.S.D.A. spokeswoman, Joelle Hayden, said in an email on Monday.
Since the outbreak of the pandemic, there have been confirmed coronavirus infections in the United States of a tiger, a lion and two pet cats. And on Tuesday, the U.S.D.A. announced that a German shepherd in New York had become the first pet dog to be tested and confirmed positive for the coronavirus in the United States. The dog is expected to recover.
One of the German shepherd’s owners has tested positive for Covid-19, and the dog had showed some signs of respiratory illness, the U.S.D.A. said. That prompted testing at a private veterinary facility, and the presumptive positive results were reported to government officials.
Those results were confirmed using swabs as well as blood tests for antibodies.
Another dog in the German shepherd’s household had showed no symptoms but was also tested and found to have coronavirus antibodies, suggesting it had been exposed to the virus.
An infection appeared possible for Winston the pug in April, when Duke University researchers studying the coronavirus visited his family at their home in Chapel Hill, N.C., and took samples from them and several of their pets.
Three of the family members — Dr. Heather McLean, Dr. Samuel McLean and their son, Ben McLean — had been infected with the virus but recovered. But the family also noticed that Winston had symptoms that made him appear ill. He was sluggish, sneezing and breathing heavily, and he didn’t finish breakfast one morning.
Winston and two other pets — Otis, 13, another pug, and Mr. Nibs, a 12-year-old tabby cat — were also swabbed by the researchers. Dr. Chris Woods, the head of the Duke University team, later said a preliminary result showed that a low amount of the virus had been detected in Winston’s saliva.
The U.S.D.A. laboratory, which carries out official confirmation of such results, then performed its own tests, and released the results on May 27. “No virus was isolated, and there was no evidence of an immune response,” Ms. Hayden said of the findings.
The “weak detection” of Winston’s original oral swab “may be the result of contamination from the Covid-19-positive household,” she added.
Many pet owners are concerned about how susceptible animals are to the coronavirus. Experts have said that there is no evidence that pets can transmit the virus to people, and that people should not worry about giving it to their pets.
The first animal that tested positive for SARS-CoV-2 in the United States was a tiger at the Bronx Zoo in April. Samples from the tiger were tested after lions and tigers at the zoo showed signs of respiratory illness, but public health officials said they believed the animals were exposed to a zoo employee who had the virus.
A lion later tested positive as well, and then the U.S.D.A. confirmed coronavirus in two pet cats. Two dogs tested positive in Hong Kong, but no dog had been verified as infected with the virus in the United States until the German shepherd was.
(The U.S.D.A. results on Winston were reported last week by WRAL, which first reported his preliminary test when contacted by the McLean family in April, and by The Canine Review, a news site about dogs.)
Dr. Woods said on Monday that Winston’s results highlighted the difference between detection of the virus and infection with it. A small amount of the virus was also found in a rectal swab later taken from the older pug, Otis, he added.
“With infection it would be replicating in him,” Dr. Woods said of Winston. “He was contaminated with it, as was his housemate.”
“These dogs would not have posed a risk to owners or other dogs or potentially to each other,” he said. “There was, at a minimum, a transient colonization event that we just happened to capture.”
“At the end of the day, I don’t want people to be scared of their animals,” he said.
Dr. John Howe, president of the American Veterinary Medical Association, said in an interview on Monday that the association was informed about the U.S.D.A. results on Winston last week.
“Winston could have licked something or someone with the virus, causing him to test positive,” he said. “But that did not mean that the virus was in his bloodstream or his respiratory tract, which would have made him infected.”
He said a dog “can have the virus in their mouth, but not in their system.”
“There was no inflammatory response,” he added.
Dr. Howe said that the veterinary association recommended that dog owners who are sick with Covid-19 wear a mask or have someone else take care of the animal.
Jacey Fortin contributed reporting.