A new dog flu virus that has killed some racing greyhounds made an unusual jump from horses to dogs and may threaten pets.
The virus can also infect dogs without making them sick, meaning it is not as deadly as some reports have suggested.
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 U.S. Centers 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.
"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 rumors 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, characterized 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.
Yet dogs could infect people with new viruses, too, the AP reports.