SPRINGFIELD, Ill. – The Illinois Department of Agriculture is reminding horse owners to vaccinate their animals before the onset of mosquito season to protect against West Nile virus (WNV).
“Many horses infected with WNV never develop the illness, but it can be very serious – even fatal – if they are not protected,” Dr. Colleen O’Keefe, IDOA division manager of Food Safety and Animal Protection, said. “During the 1999-2000 outbreak, 38% of the horses that contracted WNV died or had to be euthanized. So, I recommend that horse owners make sure their animals are properly vaccinated.”
If a horse has received annual WNV vaccinations, a booster shot is recommended before July 1. However, if the animal has never been vaccinated, two shots administered three to six weeks apart, both to be completed before July 1, are recommended to ensure optimum protection.
Vaccines that protect against Western, Eastern and Venezuelan equine encephalitis do not protect horses against encephalitis caused by West Nile virus. Therefore, even horses that are vaccinated for Western, Eastern and Venezuelan encephalitis should receive a WNV shot.
Wild birds such as crows, hawks and blue jays carry the virus, but mosquitoes spread it. The virus is retained in a mosquito’s salivary glands after it feeds on an infected bird and then injected into the blood stream of horses and other animals when the insect moves to its next meal. Horses are incidental hosts of WNV, meaning they do not transmit it.
Symptoms of WNV in horses include listlessness, lack of muscle coordination, weak limbs, partial paralysis and death. Fever has been detected in less than one-fourth of confirmed cases. The incubation period for the disease is five to 15 days.
There is no treatment for WNV. Supportive veterinary care is recommended. Suspected cases should be reported immediately to the Illinois Department of Agriculture’s Bureau of Animal Health and Welfare at (217) 782-4944.
Since the availability of an approved vaccine, the number of West Nile virus cases in Illinois has dramatically declined from 1,241 in 2002 to 21 in 2006.