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West Nile Virus and Horses

West Nile affects horses much more often than any other domestic animals. Many horses infected with West Nile do not develop any illness, but of horses that become ill about one-third die or need to be euthanized. Other livestock and poultry do not commonly show any illness if infected with West Nile.

As of Sept. 5, 2002 there have been more than 2300 equine cases of West Nile virus reported in the United States and more than 300 were reported from Minnesota.

How do horses become infected with West Nile virus?

The same way humans become infected-by the bite of infectious mosquitoes. The mosquitoes become infected after feeding on an infected bird. Mosquitoes cannot get West Nile virus from an infected horse.

Has West Nile virus caused severe illness or death in horses?

Following transmission by an infected mosquito, West Nile virus, may cause a mild transient self resolving fever or it may infect the brain causing inflammation or "encephalitis". The vast majority of horses that are bitten by infected mosquitoes do not become ill, but those that develop severe encephalitis often die.

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

West Nile virus is transmitted by infectious mosquitoes. The infected horse is not contagious to humans or to other horses. Normal infection control precautions should be followed when caring for a sick horse.

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.

My horse is vaccinated against Eastern Equine encephalitis, Western Equine encephalitis and Venezuelan Equine encephalitis. Will these vaccines protect my horse against West Nile virus infection?

No. These three viruses belong to another family of viruses for which there is no cross-protection.

Can I vaccinate my horse against West Nile virus infection?

A conditionally licensed West Nile virus vaccine for horses is available. Contact your large animal veterinarian for more information.

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. Supportive care and time are all that most horses need to fully recover.

How can I help protect myself and my family from West Nile Virus?

Horse owners should make sure that empty buckets and water troughs are not breeding sites for mosquitoes. Turn over buckets when they are not in use, and clean the water trough regularly. Make sure that faucets are turned off and do not drip.

The best way to protect you from West Nile virus, or any other mosquito-borne illness, is to reduce the number of mosquitoes around your home and neighborhood and to take personal precautions to avoid mosquito bites. These are some of the preventative steps that you can easily take:

  • Eliminate standing water where mosquitoes can breed.Check for items outside the home that collect water, such as cans, bottles, jars, buckets, old tires, drums and other containers.

  • Change water in flower vases, birdbaths, planters and animal watering pans at least twice a week.

  • Repair leaky pipes and outside faucets, and move air conditioner drain hoses frequently.

Avoid being bitten by mosquitoes when going outside at night by using insect repellent. Wear lightweight clothing that covers the arms and legs.

What if I want more information?

USDA Animal and Plant Health Inspection Service

Centers for Disease Control and Prevention

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