Four equine vaccines have been developed and approved for West Nile virus (WNV) in the past five years, one of which was the first DNA vaccine for any mammal. The pace of this progress is unheard of in industries that make vaccines for other species, and this is evidence that vaccine manufacturers and the equine veterinary community are striving to understand the efficacy of equine vaccines and their strategic use to prevent infectious disease.

Hugh G.G. Townsend, DVM, MSc, professor in Large Animal Clinical Sciences at the University of Saskatchewan, reviewed current and new technologies for vaccines and vaccination decisions at the 51st annual Convention of the American Association of Equine Practitioners (AAEP) in Seattle, Wash. He reviewed two diseases–influenza and WNV–in the presentation, because they “provide the best examples of how and where recent advances have been made in development and use.”

Influenza
Scientists have come a long way in understanding the epidemiology and control of infectious respiratory diseases. “In a little over 10 years, we’ve gone from doubting the efficacy of the equine influenza vaccines marketed in North America to knowing that most provide at least some degree of protection,” Townsend said. “These advances are the result of a significant improvement in vaccines produced by time-honored techniques as well as the introduction of vaccines formulated by new methods.”

Epidemiological studies published in 1999 and 2000 showed that in a population of Thoroughbred racehorses, outbreaks of influenza occurred once a year at about the same time. In both events, “As soon as we identified one case on the track, the outbreak took off,” Townsend explained. “Our suspicion at this time is that these (quietly starting outbreaks) represent animals that, although there is not a carrier state (for influenza), certainly can shed the virus while showing minimal clinical signs