Questions on Horses

Q: Can West Nile virus be fatal to horses?

A: Yes. West Nile virus has been identified in the tissue of several horses that died on Long Island, NY in October 1999, and specific West Nile antibody has been observed in others. Investigations by the USDA and CDC indicate that West Nile virus was responsible for some of the horse deaths.

Q: How do the horses become infected with West Nile virus?

A: The same way humans become infected - by the bite of infectious mosquitoes while biting to take blood. The virus is located in the mosquito's salivary glands. During blood feeding, the virus is injected into the blood system of the horse. The virus then multiplies and may cause illness. The mosquitoes become infected when they feed on infected birds or other animals.

Q: What actually causes the horse's death?

A: Following transmission by an infected mosquito, West Nile virus multiples 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.

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

A: 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.

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

A: No. There is no documented evidence that West Nile virus is transmitted from horse-to-horse. However, horses with suspected West Nile virus should be isolated from mosquito bites, if at all possible.

Q: 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?

A: No. EEE, WEE, and VEE belong to another family of viruses for which there is no cross-protection. There is no approved vaccine currently available for West Nile virus.

Q: How long will a horse infected with West Nile virus be infectious?

A: We do not know if an infected horse can be infectious, thereby causing 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.

Q: Should a horse infected with West Nile virus be destroyed? What is the treatment for a horse infected with West Nile virus?

A: No. 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.

Q: Is there something I can do to help protect my horse?

A: Yes. Eliminate mosquito breeding sites around the area. Maintain feeding trough drain holes, change water trough water every 3-4 days, eliminate tires from the area or cut them in half so water cannot collect in them, and eliminate standing puddles.

Frequently Asked Questions About West Nile Virus

General Questions
Questions on Illness
Questions on Birds and Reporting
Questions on Pets (Dogs, Cats, Birds)
Questions on Horses
Questions on Mosquitoes
Questions on Prevention (Mosquitoes, Environment)
Questions on DEET