The American Association of Equine Practitioners (AAEP) has released West Nile Virus (WNV) vaccination guidelines. This information is intended as a supplement to the AAEP’s Guidelines for Vaccination of Horses (January 2001). Practitioners are directed to consult this publication as the following discussion is to be read in conjunction with those general guidelines for vaccination.

West Nile virus infection was first diagnosed in horses in the United States in 1999 and is now an important consideration in the differential diagnosis of horses presenting with signs of neurologic disease in all areas of North America. West Nile virus, a flavivirus, was first identified as a cause of infection and fatal encephalomyelitis (inflammation of the spinal cord and brain) in horses and people in Egypt, Uganda and France in the early 1960’s. Further epizootics of disease in horses have occurred in Morocco in 1996, Italy in 1998, France in 2000, and the United States from 1999 to the present. West Nile virus is now considered to be endemic in all areas of North America