Curry, a 5-year-old Bichon Frisé, is one of the lucky ones. Curry recovered from canine flu, which is caused by a virus that jumped from horses to dogs in this country.

For a real-life example of influenza jumping the species barrier, look no further than the family pet. In a study published in the October 21, 2005, issue of Science, researchers reported that a decades-old variety of equine (horse) influenza has emerged in dogs.

This discovery began unfolding in 2004, when greyhounds at a Florida racetrack fell ill with an unidentified respiratory disease. Lab studies at the University of Florida failed to turn up the usual pathogens behind "kennel cough" and similar canine conditions, so researchers sent the samples to the veterinary diagnostic lab at Cornell University.

Fearing an influenza virus, Cornell scientists forwarded suspect viral samples to the U.S. Centers for Disease Control and Prevention (CDC). Sure enough, CDC staff recognized the pathogen as H3N8 equine influenza virus. Having occurred for at least 40 years in horses, this virus suddenly made a complete jump into greyhounds. Moreover, this newfound canine influenza, dubbed canine/FL/04, quickly began to spread. Since the winter of 2004 it has been confirmed in outbreaks at racetracks in at least 11 states, affecting thousands of greyhounds. Pet dogs, too, are susceptible, with confirmed cases among many breeds in Florida clinics and 16 other states, although the illness is mild in most dogs.

Nevertheless, "For scientists worried about interspecies transfer of influenza, this is a rare and striking example," says Ruben O. Donis, a CDC scientist and senior author of the Science paper. "Interspecies transmission of influenza happens quite frequently, but what we usually see is the scenario in Asia, where H5N1 avian influenza jumps to a person and then stops. That's a dead end for the virus, because it can't be transmitted from person to person. What's new, in the canine case, is the establishment of a new virus in a new host—the dog—with efficient transmission. Dogs catch this flu from other dogs. In other words, influenza has found a new host, adapted to it, and is thriving."

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Photo: AP Photo/Stuart Ramson