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Daily News Archive
From July 25, 2002

West Nile Virus Horse Vaccine

Currently, there is no vaccine available for humans against the threat of West Nile Virus. In August of 2001, however, U.S. Department of Agriculture (USDA) granted a conditional license to Fort Dodge Animal Health (FDAH) for a West Nile Virus killed-virus vaccine for use on horses. Horses, humans and birds in the crow and blue jay family are the most susceptible to a West Nile infection. The vaccine, available through licensed veterinarians, is given in two 1ml doses three weeks apart and must be revaccinated every year. Only several weeks after administration of the second dose is full antibody protection acquired.


According to www.equinewestnile.com, the vaccine was safety tested in 649 horses of various breeds, ages and sizes in five states. It has shown to be 96.28% free of local or systemic reactions. Each serial is tested to ensure there is no surviving virus in the vaccine. It has also been adjuvanted with MetaStim (tm) for enhanced efficacy. Vaccinated horses in FDAH studies developed West Nile Virus-neutralizing antibodies, as measured by the standard plaque reduction neutralization test. The antibody levels found gives a reasonable expectation of efficacy. Additional efficacy studies are in progress.


Horses cannot pass on West Nile Virus to other organisms. "We call horses dead-end hosts because they cannot pass this virus to other horses, humans, or mosquitoes," said Dr. John Berends, equine reproductive specialist and MSU Extension veterinarian. Unlike Eastern Equine Encephalitis (EEE) and Western Equine Encephalitis (WEE) which have a very low survival rate, clinically affected horses appear to have a 65 percent chance of recovery and return to normal function when treated. Although there is an existing equine vaccine for both EEE and WEE there is no cross over protection from West Nile Virus.