A strain of flu virus that jumped from horses to dogs has caused sometimes deadly respiratory infections at dog tracks and kennels in at least 11 states and among some household pets as well, health officials reported Monday.

While cautioning dog owners to keep their pets away from other dogs if they have a respiratory infection to try to minimize further spread of the virus, experts said most dogs recover from the infection.

The discovery comes as public health officials are increasingly alarmed about a dangerous strain of flu that has been spreading among birds in Asia and occasionally infecting humans, but there is no evidence that the dog virus can spread to humans.

''We are going to monitor all cases of human exposure, but at this point there is no reason to panic,'' said Ruben Donis of the federal Centers for Disease Control and Prevention in Atlanta. Donis noted that the virus has been known to cause the flu in horses for about 40 years without any reports of infecting humans. Tests also indicate it is sensitive to anti-viral drugs.

The CDC held a news briefing to discuss the virus to coincide the release of a paper by the journal Science documenting the identification of the virus.

Researchers predicted the number of states with documented infections will increase rapidly because veterinarians are just now becoming aware of the new virus.

Since the virus is new to dogs, most would have little immunity against it. The virus presumably spreads among dogs by an infected animal sneezing or coughing on another.