A recent study at Colorado State University (CSU) found that your horse might have the ability to fight off West Nile virus (WNV) less than a month after receiving a single-dose vaccination against the disease. The challenge study tested Merial’s RECOMBITEK equine WNV vaccine 26 days after immunization and found that the treated horses resisted infection.

The results are particularly important for horse owners and veterinarians in areas prone to sudden natural WNV outbreaks, where early immunity could mean the difference between life and death for horses.

“If you put yourself in the place of someone in California, where West Nile suddenly appears in an area, you’d like to have a vaccine with rapid immunity–you don’t want to wait two months,” said study co-author Dick Bowen, DVM, PhD, associate professor in the department of biomedical sciences at CSU. “The study basically showed that the vaccine, in a single dose, elicits good immunity early on.”

The study, published in the November 2004 issue of the American Journal of Veterinary Research, involved challenging nine immunized horses (which had received one dose of RECOMBITEK) with virulent WNV-infected mosquitoes. A control group of 10 horses, also challenged with the WNV-infected mosquitoes, did not receive the vaccine. None of the horses in the study had experienced prior exposure to WNV.

Study results showed that eight of the nine inoculated horses were protected from infection (viremia) within 26 days of vaccination, while eight of the 10 control horses developed viremia (clinical signs of disease were observ