By Maggie Fox
Washington - A new dog flu virus that has killed some racing greyhounds made an unusual jump from horses to dogs and may threaten pets but not people, experts said on Monday.
And the virus can also infect dogs without making them sick, meaning it is not as deadly as some reports have suggested, they said.
But studying it has important implications for understanding the H5N1 avian flu virus now devastating flocks of poultry and which has killed 65 people in four Asian nations since late 2003.
The new dog virus is an influenza A virus called H3N8, a designation that describes two important proteins in the virus.
There is no evidence that it can infect people, said Dr Ruben Donis of the United States Centre for Disease Control and Prevention, who has published a report on the new virus in the journal Science.
"We must keep in mind that this H3N8 equine influenza virus has been in horses for over 40 years.
"In all these years we have never been able to document a single case of human infection with this virus," Donis told reporters in a telephone briefing.
"At this point there is no reason to panic," he said, adding that in lab dishes, anyway, the virus could be controlled with antiviral drugs."
Dr Cynda Crawford of the University of Florida College of Veterinary Medicine first discovered the virus in greyhounds. It looked deadly at first.
"This virus can cause a respiratory disease that mimics a syndrome that we call kennel cough," Crawford told reporters.
"Kennel cough can be due to a myriad of infectious agents," she added, with a bacterial infection called Bordetella the most common cause.
Further checks have found the virus in dogs that were both ill and that seemed entirely healthy in Florida, New York and Massachusetts.
"Despite the rumours that are out on the Internet, this disease is not as deadly as people want to make it.
"Nearly all dogs are susceptible to infection... about 80 percent of them will have a mild form of disease, characterised by cough and some nasal discharge that will resolve," she said.
It seems to have a mortality rate of between 5 and 8 percent, she said.
Donis said very few changes in the virus, in just a few of the amino acid building blocks of proteins, seemed to have allowed it to jump species from horses to dogs.
This was an "an unprecedented interspecies transfer", he said - and would have implications for understanding the potential of H5N1 to begin infecting people easily.
And dogs could infect people with new viruses, too, the researchers theorised.
"Evidence of canine influenza infection in pet dogs, a primary companion animal for humans, raises the possibility that dogs may provide a new source for transmission of novel influenza A viruses to humans," they wrote in the Science report.
Crawford said pet owners did not need to be unduly concerned yet.
"I am taking my two Pekinese to be groomed next week. I will continue to board my pet greyhounds at boarding kennels when I need to," she said.
She will even let her dogs play at dog parks, but said owners should exercise common sense and keep their pets inside when they have any respiratory disease for two weeks or so, both to allow them to fully recover and to protect other dogs.