Built for speed. A new flu virus, which first appeared among U.S. race dogs, is spreading fast among canines.

Flu Virus Jumps from Horses to Dogs

Mankind may be worried about a worldwide outbreak of influenza, but man's best friend is already in the midst of one. A dangerous flu virus that originated in horses is spreading fast among U.S. dogs and may circle the globe, researchers say. While the outbreak poses no direct threat to humans, "it's another example of what we fear most about flu viruses: They're always trying out new hosts," says Michael Perdue, an animal influenza expert at the World Health Organization in Geneva, Switzerland.

The current outbreak, described in a paper published online by Science today came to light after 22 greyhounds developed a respiratory disease--and eight died--at a Florida racetrack in January 2004. Cynda Crawford, an immunologist at the University of Florida's College of Veterinary Medicine in Gainesville, sent tissue samples from the infected dogs to Edward Dubovi at Cornell University in Ithaca, New York, who isolated the influenza virus. A team led by Ruben Donis at the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, then typed and sequenced the virus. The researchers found that it belongs to the H3N8 strain, which causes influenza in horses worldwide.

The virus appears to be spreading fast. Last year, 14 greyhound racetracks in six U.S. states reported respiratory outbreaks; in 2005, 20 tracks in 11 states did. Although the team did not investigate every outbreak, it found evidence of H3N8 wherever it looked. The team also reports that almost 80% of 70 dogs with respiratory disease in veterinary clinics and shelters in Florida and New York City were infected.

Whatever triggered the leap from horses to dogs, nothing seems to stand in the way now of a 'panzootic,' Donis says--the animal equivalent of a pandemic. Perdue says current horse vaccines should be easy to adapt for dogs and may be available soon.

Theoretically, the canine outbreak also gives the virus new chances to enter the human population. So far, there's no sign it has; nor has the virus been known to jump from horses to humans, says Thomas Chambers, an equine influenza expert at the University of Kentucky in Lexington. The CDC researchers plan to test people who were in contact with sick dogs as soon as they have approval from an ethics panel. If any of them turns out to be infected--even asymptomatically--says Perdue, "that would raise a big red flag."

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