The Virginia Department of Agriculture and Consumer Services (VDACS) today announced 2011’s first positive case of West Nile Virus (WNV) in a horse. The horse was from Berryville/Clarke County. It had been vaccinated for WNV but was due for a booster in September.
A nasal swab and serum sample was submitted to VDACS’ Regional Animal Health Laboratory in Warrenton for suspicion of Equine Herpes Virus infection, but it tested positive for West Nile Virus. Onset of symptoms was August 30. The horse was treated for symptoms – low-grade fever, ataxia, hypermetria (lifting its feet excessively high) and intermittent central nervous system depression – for 24 hours and then euthanized on August 31.
Dr. Joe Garvin, head of VDACS’ Office of Laboratory Services, urges horse owners to check with their veterinarians about vaccinating their animals for WNV. “This is our first case of West Nile Virus in a Virginia horse this year,” Garvin said. He adds that, so far, Virginia has not had any cases of Eastern Equine Encephalitis (EEE). “Both WNV and EEE are mosquito-borne diseases,” he said, “and we generally start seeing our first cases in August and September. Since both diseases are preventable by vaccination, it may make sense for horse owners to go ahead and vaccinate now even though it’s late in the year. 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.
The virus usually lives in wild birds of many different species. Mosquitoes transmit it 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 West Nile Virus and other mosquito-borne diseases.
Currently, no drugs exist to treat WNV specifically in horses or humans. 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.
WNV can cause a horse to go down and be unable to get up without help. Animal owners should consult their veterinarians if an animal exhibits any neurological symptoms such as a stumbling gait, 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.