What is West Nile virus (WNV)?

West Nile is a type of virus that causes encephalitis, or inflammation of the brain. The virus has been found in Africa, western Asia, the Middle East, the Mediterranean region of Europe and recently in the United States. Mosquitoes become infected with the virus after feeding on infected wild birds and then transmit the virus through bites to people, animals and other birds.

What are the signs and 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 (in-coordination), 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 your veterinarian. Only laboratory tests can confirm the diagnosis of West Nile encephalitis.

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 suggests that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.

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.

Can I get infected with West Nile virus by caring for an infected horse?

Infected mosquitoes transmit WNV to people through blood feeding. There is no documented evidence of person-to-person, or animal-to-person transmission of WNV.

Can a horse infected with West Nile virus infect horses in neighboring stalls?

No. There is no documented evidence that WNV is transmitted from horse-to-horse. Horses with suspected WNV if possible should be protected from additional mosquito bites.

Is there a West Nile Virus vaccine for horses?

A West Nile virus vaccine for horses was recently approved, but its effectiveness is unknown.

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 are alphaviruses. West Nile is a flavivirus. There is no cross-protection.

For further information:

That West Nile Thing - Natural Care Series

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