Horses and West Nile Virus

The University of California Davis Center for Equine Health is recommending that California horse owners should have their horses vaccinated for West Nile virus starting in March/April 2006, before the summer's peak mosquito season. There is an estimated one million horses in California. The mortality rate in horses that contract West Nile virus remains at about 30 percent.

A horse vaccine became available in 2001, under conditional approval by the U.S. Department of Agriculture. The vaccine, made by Fort Dodge Animal Health, was granted full approval in 2002. According to the company, it has been found effective in warding off the illness in horses with 95 percent efficiency.

U.C. Davis Center for Equine Health :

• Vaccinate all previously non-vaccinated adult horses in March/April 2006 with a two-dose primary series, 3 to 4 weeks apart.
• As a general rule, UC Davis veterinarians recommend that you avoid vaccinating pregnant mares in the first trimester of gestation whenever possible. Talk to your veterinarian about your best options for vaccinating your particular mare.
• Vaccinate all young horses (less than one year of age) in March/April 2006 with a three-dose primary series. Allow 3 to 4 weeks between doses one and two, and allow 6 to 8 weeks between doses two and three.
• If the foal was born to a mare or a mare that was not booster vaccinated 4 to 6 weeks before foaling, begin the vaccination series at 3 months of age.
• If the foal was born to a mare that was booster-vaccinated within 2 months of foaling, then begin the vaccination series at 4 to 6 months of age.
• Vaccinated Horses - If your horse was fully vaccinated last year or if the primary vaccination series was completed this year, follow up with a booster every six months.
• Booster all horses that have not been vaccinated within the previous 6 to 8 weeks, then follow with boosters every 6 months from the date of the last vaccination.