The 13-year-old mixed breed male, which is recovering, apparently caught the virus from its owner. But Michael San Filippo, a spokesman for the American Veterinary Medical Association, said there's no evidence that the flu strain can be transmitted from a pet to a person.
"In theory it could happen, but so far it's really looking like a dead end in pets," he said.
Dr. Anne Schuchat of the federal Centers for Disease Control and Prevention said Tuesday that animals can carry and spread flu viruses, but such cases are rare and people should not be afraid to enjoy their pets.
The CDC reported this month that swine flu appears to be waning among humans. It said infections were widespread in 25 states, down from 48 in late October.
San Filippo said the diagnosis of the 2009 H1N1 virus was confirmed at two labs, including Iowa State University's.
The dog, suffering breathing problems, was taken to the Katonah Bedford Veterinary Center in Bedford Hills, New York, on Dec. 13.
The medical director there, David Sachs, said he had the dog tested for swine flu because its owner previously had the virus. The practice would not identify the owner or give the dog's name.
The maker of the test, Idexx Laboratories, said it determined the test was positive and sent it to the veterinary lab at Iowa State for confirmation.
Among pets, cats and ferrets have previously been found to catch the swine flu strains from humans, and at least one cat and one ferret have died, San Filippo said.
By Associated Press Writer Jim Fitzgerald; AP Medical Writer Marilynn Marchione contributed to this report