The Virginia Department of Agriculture and Consumer Services (VDACS) announced on Sept. 28 the state's first positive case of West Nile virus (WNV) in a horse this year. The horse, an 8-year-old Paint gelding, is from Augusta County. It had not been vaccinated for WNV.
Dr. Joe Garvin, head of VDACS’ Office of Laboratory Services, urges horse owners to check with their veterinarians about vaccinating their animals for WNV. “WNV is a mosquito-borne disease,” he said, “and we generally start seeing our first cases in August and September. The disease is preventable by vaccination, as is Eastern equine encephalitis, so many veterinarians recommend vaccination at least yearly, and in mosquito-prone areas, every six months.” He adds that mosquito season in Virginia can run through November.
The WNV vaccine for equines initially requires two doses administered three to six weeks apart. The vaccine takes four to six weeks from the second dose for optimal effectiveness. Horse owners should consult with their veterinarians to choose a re-vaccination schedule to protect their horses effectively. Prevention methods besides vaccination include destroying standing water breeding sites for mosquitoes, use of insect repellents and removing animals from mosquito-infested areas during peak biting times, usually dusk to dawn.
Mosquitoes can transmit the virus from bird to bird. Occasionally a mosquito that has bitten an infected bird will then bite a human, horse or other mammal and transmit the virus to them. Transmission between horses and humans is extremely unlikely. Continuous, effective mosquito control can minimize the risk of exposure of both horses and humans to mosquito-borne diseases.
Currently, no drugs exist to treat WNV specifically in horses or humans. The mortality rate in equines is about 30%. Treatment for an infected horse consists of supportive therapy to prevent the animal from injuring itself throughout the two to three weeks of the disease. A veterinarian can prescribe treatment tailored to the particular case.
Animal owners should consult their veterinarians if an animal exhibits any neurological symptoms such as a stumbling gait, going down, facial paralysis, drooping or disinterest in their surroundings. Currently, there are live-animal tests for WNV in horses and chickens, but none for other animals, although testing can be done on any dead animal. Animal owners should consult their veterinarians or the nearest VDACS Regional Animal Health Laboratory for advice or information should an animal exhibit symptoms of WNV. The location and phone number of each lab is available at vdacs.virginia.gov/about/directory-ais.shtml.
The following websites provide more information on WNV and how to protect humans and horses: