Researchers recently identified a highly contagious canine influenza virus strain that is thought to be an adaptation of an equine flu strain, which was transferred from horses to dogs in 2004. It is unclear at this time whether the strain can re-infect horses.

Scientists from the Colleges of Veterinary Medicine at the University of Florida (UF) and Cornell, along with the Centers for Disease Control and Prevention (CDC), published a paper on the topic that appeared Sept. 29 in Science Express online.

The strain first surfaced in dogs at a Florida Greyhound racetrack in January 2004. Ruben Donis, PhD, chief of molecular genetics for the CDC’s influenza branch, said, “Horses acquired the H3N8 influenza virus from an unknown species, perhaps an aquatic bird, in 1963. During the past 40 years, the virus circulated the horse population worldwide, adapting progressively to this species by a process of mutation and selection.

“The virus might have just recently reached the high level of adaptation to mammalian host that was necessary for infection of dogs,” Donis explained. He called the illness’ emergence “a very rare event of considerable scientific interest with regards to understanding influenza virus transmission across species barriers