Horse News & Views - May 2002

Ministry of Agriculture, Food and Rural Affairs

Ontario Association of Equine Practitioners

• Spring is herd health time, when owners and veterinarians are getting horses ready for the busy show and racing seasons. We are already receiving inquiries regarding the need for vaccination for Eastern Encephalitis (EEE) and Western Encephalitis (WEE), better known as "sleeping sickness" and West Nile Virus (WNV). Sleeping sickness occurs sporadically in Ontario horses. In the fall of 2001, two horses with clinical signs were confirmed as infected, one in the South Muskoka area and another that had been in competitions in the same area (Dr. Tom Wilson, Canadian Food Inspection Agency). These diseases are transmitted to horses and humans by mosquitoes that have fed on diseased birds. They cause swelling of the brain, resulting in staggering, convulsions, and fever. For further information on these diseases and their prevention, refer to the information sheets, Equine Viral Encephalitis and West Nile Virus Threat to Ontario Horses at http://www.omafra.gov.on.ca/english/livestock/horses/westnile.htm
• In areas where equine encephalitis (WEE/EEE) viruses are a risk, adult horses should be initially vaccinated with two doses of vaccine four weeks apart. Pregnant mares should be vaccinated four to six weeks before foaling to enhance colostral immunoglobulin transfer to the foal. Foals should be vaccinated starting at four months of age. An initial series of three doses, four to six weeks apart, is recommended by the American Association of Equine Practitioners. (AAEP Guidelines for Vaccination of Horses, January 2001).