West Nile virus
West Nile virus is a mosquito-borne disease of birds that was first detected in the U.S. in 1999. It has steadily moved west and late in 2002 the disease was confirmed in 2 birds and 2 horses in Washington State. The Centers for Disease Control and Prevention have predicted that the West Coast will probably be hit hard with West Nile Virus in 2004.
This virus is spread by mosquitoes when they feed on infected birds. There are at least 6 known species of mosquitoes in our region that can transmit this virus. Our mosquito season generally runs from March through October, peaking in August and September.
Although the virus does not affect most humans and horses, it should be considered a serious threat. The virus normally induces mild symptoms, but it can cause encephalitis, an inflammation of the brain, or lining of the brain and spinal cord. The virus can affect all equines, including horses, mules, and donkeys.
Symptoms in Horses
Most horses are not affected by the virus and do not show signs of illness. Look for two or more of these symptoms: loss of appetite, fever, difficulty walking (stumbling, knuckling over, falling), head tilt, muscle tremors and weakness, depression, hypersensitivity, paralysis, and convulsions. The mortality rate in horses that contract West Nile virus is about 30%. Approximately 40% of the horses that recover will exhibit some residual affects of the disease, such as neurological or behavioral abnormalities.
There are two vaccines available to provide protection against West Nile virus for horses, mules and donkeys. In addition to Fort Dodge Animal Health’s West Nile Innovator approved by USDA in 2002, a new vectored modified live vaccine was recently approved. The new product, using recombinant DNA technology, Recombitek Equine West