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Has West Nile virus caused severe illness or death in horses?
Yes, while data suggest that most horses infected with West Nile virus recover, results of investigations indicate that West Nile virus has caused deaths in horses in the United States.

 How do the horses become infected with West Nile virus?
The same way humans become infected—by the bite of infectious mosquitoes. The virus is located in the mosquito's salivary glands. When  mosquitoes bite or "feed" on the horse, the virus is injected into its blood system. The virus then multiplies and may cause illness. The mosquitoes become infected when they feed on infected birds or other animals.

How does the virus cause severe illness or death in horses?
Following transmission by an infected mosquito, West Nile virus multiplies in the horse's blood system, crosses the blood brain barrier, and infects the brain. The virus interferes with normal central nervous system functioning and causes inflammation of the brain.

Can I get infected with West Nile virus by caring for an infected horse?
West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus. Normal veterinary infection control precautions should be followed when caring for a horse suspected to have this or any viral infection.

Can a horse infected with West Nile virus infect horses in neighboring stalls?
No. There is no documented evidence that West Nile virus is transmitted between horses. However, horses with suspected West Nile virus should be isolated from mosquito bites, if at all possible.

My horse is vaccinated against eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE). Will these vaccines protect my horse against West Nile virus infection?
No. EEE, WEE, and VEE belong to another family of viruses for which there is no cross-protection.

How long will a horse infected with West Nile virus be infectious?
We do not know if an infected horse can be infectious (i.e., cause mosquitoes feeding on it to become infected). However, previously published data suggest that the virus is detectable in the blood for only a few days.

What is the treatment for a horse infected with West Nile virus?  Should it be destroyed?
There is no reason to destroy a horse just because it has been infected with West Nile virus. Data suggest that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.

What are the signs and the symptoms of West Nile encephalitis in horses?
In horses that do become clinically ill, the virus infects the central nervous system and causes symptoms of encephalitis. Clinical signs of encephalitis in horses include loss of appetite and depression, in addition to any combination of the following signs ‹ fever, weakness or paralysis of hind limbs, muscle fasciculations or muzzle twitching, impaired vision, ataxia (incoordination), head pressing, aimless wandering, convulsions, inability to swallow, circling, hyperexcitability, or coma.
It is important to note that not all horses with clinical signs of encephalitis have West Nile encephalitis.
Other diseases, including rabies, botulism, equine protozoal myeloencephalitis (EPM), and other mosquito-borne viral encephalitic diseases of horses caused by Eastern, Western, and Venezuelan encephalitis viruses, can cause a horse to have symptoms similar to WNV. If you are concerned your horse may be exhibiting signs of encephalitis, please contact the Ohio Department of Agriculture or your veterinarian. Only laboratory tests can confirm the diagnosis of West Nile encephalitis.

Is there a vaccine to protect my horse from West Nile Virus?
Currently, there is a vaccine available against West Nile Virus. It is imperative that horses are vaccinated twice, three to six weeks apart initially, with this vaccine. Horses should have two boosters annually in April and late July. Horses vaccinated against Eastern, Western, and Venezuelan equine encephalitis are not protected against West Nile Virus.