Daily News Archive
July 25, 2002
West Nile Virus
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
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.