Over the course of a few short months, the Australian horse flu outbreak cost the country approximately $100 million AU ($92.6 million US) and caused racing, breeding, and other performance horse-related activities to effectively grind to a halt.

Australia, which was influenza-free until August 2007, was hard hit by this virus. The combination of a naïve population (one with no immunity or prior exposure) and a virus that is easily spread is a recipe for disaster, which was clearly demonstrated in the Australian outbreak.

The horse flu is caused by influenza A virus strain, subtype H3N8. Vaccines are available against this virus subtype; however, the vaccine is not able to completely protect horses from becoming infected with the horse flu.

"No vaccine is 100% effective," explained Scott Weese, DVM, DVSc, Dipl. ACVIM, from the Ontario Veterinary College at the University of Guelph in Canada. "Some horses may not mount a protective immune response after vaccination, assuming the horse is actually exposed to the strain of influenza in the vaccine

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