A new, highly contagious and sometimes deadly canine flu is spreading in kennels and at dog tracks around the country, veterinarians said yesterday.

The virus, which scientists say mutated from an influenza strain that affects horses, has killed racing greyhounds in seven states and has been found in shelters and pet shops in many places, including the New York suburbs, though the extent of its spread is unknown.

Dr. Cynda Crawford, an immunologist at the University of Florida's College of Veterinary Medicine who is studying the virus, said that it spread most easily where dogs were housed together but that it could also be passed on the street, in dog runs or even by a human transferring it from one dog to another. Kennel workers have carried the virus home with them, she said.

How many dogs die from the virus is unclear, but scientists said the fatality rate is more than 1 percent and could be as high as 10 percent among puppies and older dogs.

Dr. Crawford first began investigating greyhound deaths in January 2004 at a racetrack in Jacksonville, Fla., where 8 of the 24 greyhounds who contracted the virus died.

"This is a newly emerging pathogen," she said, "and we have very little information to make predictions about it. But I think the fatality rate is between 1 and 10 percent."

She added that because dogs had no natural immunity to the virus, virtually every animal exposed would be infected. About 80 percent of dogs that are infected with the virus will develop symptoms, Dr. Crawford said. She added that the symptoms were often mistaken for "kennel cough," a common canine illness that is caused by the bordetella bronchiseptica bacteria.

Both diseases can cause coughing and gagging for up to three weeks, but dogs with canine flu may spike fevers as high as 106 degrees and have runny noses. A few will develop pneumonia, and some of those cases will be fatal. Antibiotics and fluid cut the pneumonia fatality rate, Dr. Crawford said.

The virus is an H3N8 flu closely related to an equine flu strain. It is not related to typical human flus or to the H5N1 avian flu that has killed about 100 people in Asia.

Experts said there were no known cases of the canine flu infecting humans. "The risk of that is low, but we are keeping an eye on it," said Dr. Ruben Donis, chief of molecular genetics for the influenza branch of the Centers for Disease Control and Prevention, which is tracking the illness.

But with the approach of the human flu season and fears about bird flu in Asia, there is much confusion among some dog owners who have heard about the disease.

Dr. Crawford said she was fielding calls from kennels and veterinarians across the country worried that they were having outbreaks.

"The hysteria out there is unbelievable, and the misinformation is incredible," said Dr. Ann E. Hohenhaus, chief of medicine at the Animal Medical Center in New York.

Dr. Hohenhaus said she had heard of an alert from a Virginia dog club reporting rumors that 10,000 show dogs had died.

"We don't believe that's true," she said, adding that no dogs in her Manhattan hospital even had coughs.

Dr. Donis of the disease control centers said that there was currently no vaccine for the canine flu. But he said one would be relatively easy to develop. The canine flu is less lethal than parvovirus, which typically kills puppies but can be prevented by routine vaccination.

Laboratory tests, Dr. Donis said, have shown that the new flu is susceptible to the two most common antiviral drugs, amantidine and Tamiflu, but those drugs are not licensed for use in dogs.

The flu has killed greyhounds at tracks in Florida, Massachusetts, Adminzona, West Virginia, Wisconsin, Texas and Iowa. Tracks and kennels have been forced to shut down for weeks for disinfection.

In Chestnut Ridge, north of New York City, about 88 dogs became sick by early September, and 15 percent of those required hospitalization, said Debra Bennetts, a spokeswoman for Best Friends Pet Care, a chain of boarding kennels. The kennel was vacated for decontamination by Sept. 17.

About 17 of the infected dogs were treated at the Oradell Animal Hospital in Paramus, N.J., where one died and two more were still hospitalized, a staff veterinarian said.

The Best Friends chain owns 41 other kennels in 18 states, and no others have had an outbreak, Dr. Larry J. Nieman, the company's veterinarian, said.

In late July, at Gracelane Kennels in Ossining, N.Y., about 35 dogs showed symptoms, said the owner, Bob Gatti, and he closed the kennel for three weeks to disinfect.

About 25 of the dogs were treated by an Ossining veterinarian, Glenn M. Zeitz, who said two of them had died.

"The dogs came in very sick, with high fevers and very high white blood cell counts," Dr. Zeitz said, making him suspicious that they had something worse than kennel cough.

A spokesman for the New York City Health Department said that there were "a few confirmed cases" in New York but that the city was not yet tracking the disease.

Veterinarians voluntarily sent samples to the Animal Health Diagnostic Center at the Cornell School of Veterinary Medicine, which was the only laboratory doing blood tests.