Timely through August 31, 2002
CONTACT: Ann Bailey Berry, WVU Extension Communications
Phone: (304) 293-4221, ext. 3416; e-mail: Ann.Berry@mail.wvu.edu
Robert E. Pitts, Extension Veterinarian
Phone: (304) 293-2631, ext.4439; e-mail: Bob.Pitts@mail.wvu.edu
West Nile virus, which was recently found in an Eastern Bluebird in Jackson
County, is of special concern for horse owners in the state. The virus causes
encephalitis in horses.
The West Nile virus has existed for years in Africa, Asia and Southern Europe. The virus was first identified in the United States in 1999. Since then, the virus has been found in 28 states and the District of Columbia.
Birds are the reservoir for this virus. When a female mosquito feeds on an infected bird, the mosquito picks up the virus through the ingested blood. The virus locates in the salivary glands of the mosquito. When the mosquito feeds on another bird, the virus is spread and replicates. Most birds become infected, develop immunity and overcome the infection, but others, especially crows and blue jays, die from the infection.
Unfortunately, the mosquito, which is carrying the virus, may feed on a horse. The horse is an end host for the virus, since numbers of virus particles in the blood do not become high enough for the horse to become a source of infection for other mosquitoes.
The virus causes encephalitis in horses. The clinical symptoms may include neurological disorders such as ataxia, depression, loss of appetite, hind limb weakness or death. Approximately 40 percent of the horses that become infected die. Only supportive treatment is available.
Until last year, the only means of preventing this disease in horses was to limit exposure to mosquitoes through management and removal of mosquito breeding sites to lower the number of mosquito vectors and the risk of infection.
Last year, a conditional license for a killed West Nile virus vaccine for horses was approved. It is recommended that the horse initially receive two doses, three to six weeks apart, and an annual booster. The vaccine should be given at least three weeks before the mosquito season. Use of the vaccine appears to be relatively safe, with 98.5 percent of the vaccinated animals not having any severe local or systemic reactions.
Horse owners should be concerned about this threat to their horses and contact their veterinarian for recommendations.
--WVU-ES--
REP-7/26/02
