EquiRab Rabies Vaccine Effective in Study (AAEP 2009)

Rabies is one of those diseases you want to avoid at all costs--it's rapidly progressive, fatal, and can be transmitted from your horse (or any other infected animal) to you. While vaccines are available for horses, no data was published on their efficacy in the literature until December 2009.

At the 2009 American Association of Equine Practitioners (AAEP) Convention, held Dec. 6-10 in Las Vegas, Nev., a study on the efficacy of the EquiRab rabies vaccine was presented by Craig Barnett, DVM, equine technical services veterinarian at Intervet/Schering-Plough Animal Health.

"Rabies surveillance shows about 7,000 cases of rabies annually (in the United States), mostly in wildlife, but also 30-50 cases of equine rabies per year," Barnett said. "These numbers represent only a fraction of what's actually out there."

For this study, which was done as part of the registration requirements to license the vaccine, 26 horses were vaccinated with EquiRab (single 1-mL dose) and 11 served as unvaccinated controls. "All vaccinated horses developed high levels of rabies virus-neutralizing antibody that persisted for at least 12 months," Barnett reported. In addition, horses with the lowest antibody levels were challenged with injected rabies virus 14 months after vaccination. No vaccinated horses developed disease, but 80% of the unvaccinated controls did.

Barnett also noted that all vaccinated horses had increased levels of antibodies against rabies virus as quickly as seven days after vaccination. "That started me thinking about postexposure treatment," he commented. "There was a study published in the Journal of the American Veterinary Medical Association (Wilson 2001) that looked at postexposure rabies vaccination used in Texas according to state law (vaccinate immediately, isolate and observe for 90 days, and booster during the third and eighth weeks of isolation). In that study, the records of 830 unvaccinated, exposed animals that followed this protocol were reviewed. Only four cases developed rabies, and they were all dogs. Texas is the only state I know of that allows this protocol; maybe other states should look at that as an option for exposed horses."

One attendee asked after the presentation if the vaccine's efficacy had been proven effective after a long enough period to allow vaccination less often than once per year. Barnett answered, "The vaccine has not been proven to be effective beyond the 14-month duration of immunity (DOI) that is on the label. Expansion of the label to include a longer DOI would require challenging vaccinated horses in a quarantine facility at the designated time (i.e., three years) post-vaccination; such a study has not been done. Considering the seriousness of this disease and the potential public health significance, I would not recommend extending the vaccination interval beyond what is on the label.

"Rabies is a core vaccine as defined by the AAEP, and it should be strongly considered for all equine patients," Barnett concluded.

For more information see AAEP Rabies Vaccination Guidelines (AAEP Rabies Vaccination Guidelines).

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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