Dogs Also Victims of 2007 Equine Influenza in Australia

Australian officials confirmed that the equine influenza virus infecting about 20,000 horses in the country in 2007 also infected dogs that had close contact with the sick horses.

"Dogs that were with or near equine influenza-infected horses were observed with a flu-like illness," said Peter D. Kirkland, PhD, of the Elizabeth Macarthur Agricultural Institute in New South Wales, Australia. "Detailed genetic studies [of samples] showed the responsible virus was identical to the virus in the horses. If horse owners want to protect their dogs from canine influenza, they should keep dogs away from close contact with infected horses."

The exposed dogs came down with flu-like symptoms, including a harsh cough, nasal discharge, lethargy, and refusal to eat. Although some dogs became quite sick for a short time, none of the dogs died, which differs from the experience in the United States, Kirkland said.

In the U.S., canine influenza H3N8 virus (CIV) is a highly contagious canine respiratory infection that has been confirmed in 30 states and the District of Columbia.

"Molecular analyses of CIV isolates support their origination from the interspecies transmission of equine influenza A H3N8 viruses from horses to dogs as early as 1999," said Cynda Crawford, DVM, PhD, of the University of Florida.

The U.S. virus mutated to become a canine-specific pathogen that is transmitted from dog to dog. However, the virus did not spread from dog to dog in Australia.

So far, canine influenza H3N8 cases have not been seen outside of the U.S., Crawford said, adding that experimental studies have shown that horses are susceptible to CIV infection, but the infection induces either no or mild clinical disease.

A CIV vaccine (Intervet/Schering Plough Animal Health) is available in the U.S. The vaccine is a "lifestyle" vaccine for dogs at risk for exposure and should be considered for dogs in contact with horses.

The report, "Influenza virus transmission from horses to dogs in Australia," was published in the April issue of Emerging Infectious Diseases. The abstract is available on PubMed.

About the Author

Marie Rosenthal, MS

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