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West Nile Virus in Horses

West Nile Virus (WNV) is a relatively new disease in horses in the United States, first arriving in 1999 from Asia, Europe, and the Middle East via infected mosquitoes. This virus can affect both humans and horses, posing significant health risks.

How Do Horses Get West Nile Virus?

Horses contract West Nile Virus through the bite of an infected mosquito. These mosquitoes acquire the virus by feeding on infected wild birds. When a mosquito with the virus bites a horse, it injects the virus into the horse's bloodstream. It's important to note that horses do not spread WNV to other horses or humans. Horses are not a reservoir of the virus, and touching an infected horse does not transmit the virus to others.

Signs of Equine WNV

Most WNV infections in horses are mild, presenting symptoms such as fever and loss of appetite. These horses typically recover within a few days. However, about one-third of infected horses experience moderate to severe symptoms, which can be life-threatening. Moderate symptoms include muscle tremors, stumbling, and incoordination. Severe symptoms, resulting from an inflamed central nervous system and muscles, include the horse sitting like a dog, being unable to stand, or lying down completely. In some cases, these severe symptoms can lead to death. The incubation period for WNV in horses is 3 to 15 days after the mosquito bite.

Equine Encephalitis

West Nile Virus can cause encephalitis, an inflammation of the central nervous system, in horses. There are three viral encephalitis forms in horses: Eastern Equine Encephalitis, Western Equine Encephalitis, and West Nile Encephalitis. Younger and older horses are particularly susceptible to the virus.

West Nile Treatment in Horses

Treatment for West Nile Virus in horses primarily involves supportive care. There are no specific antiviral treatments or immunoantibody serums available. Prevention through vaccination is crucial, as severe cases often result in death.

Prevention with the West Nile Vaccine for Horses

Vaccination is the most effective way to protect horses from West Nile Virus. The initial vaccination involves a series of two doses, given three to six weeks apart. The horse will be protected from WNV four to six weeks after the second dose. After the initial series, an annual booster shot is sufficient to maintain immunity. Vaccinating your horse is a cost-effective measure to ensure its health and well-being.

Mosquito Protection for Horses

In addition to vaccination, mosquito control is essential. Here are some tips to protect your horse from mosquito bites:

  • Spray Horses: Apply mosquito repellent sprays to horses twice a day, in the morning and evening.

  • Eliminate Standing Water: Remove any containers or areas where water can accumulate, as these are breeding grounds for mosquitoes.

  • Discourage Birds: Limit the presence of wild birds around your stable, as they can carry the virus.

  • Use Environmental Sprays: Use environmentally safe sprays to control the mosquito population around your stable.

By taking these preventive measures, you can significantly reduce the risk of West Nile Virus infection in your horses.

For more information on West Nile Virus in horses and other equine health concerns, visit

West Nile Virus in Horses
West Nile Virus in Horses


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