West Nile Virus (WNV)

What is West Nile Virus(WNV)?

West Nile Virus is a vector-borne (mosquito) neurological disease affecting horses. WNV was first recognized in North America in 1999 and has spread over much of the United States and Canada since that time.

What are the clinical signs of WNV?

Clinical signs of WNV can be quite variable between horses and can include: fever, depression and a reluctance to eat. Some horses will progress to neurological signs including: muscle tremors, ataxia and drowsiness. Mortality rates can reach between 30-40%.

Are there any human health risks?

While infected mosquitos can pass WNV on to humans, direct contact between humans and horses cannot spread the disease.

How is WNV transmitted?

Migrating wild birds often provide the viral reservoir for the disease. Mosquitos become infected when feeding on such birds. WNV is then transmitted to horses when bitten by infected mosquitos.

How is WNV diagnosed and treated?

The clinical signs of infection are not specific to WNV so blood tests need to be performed for a definitive diagnosis. There is no specific treatment for the disease, supportive care is offered to help reduce pain and inflammation for the horse and to prevent injuries. Horses that do not succumb to disease recover over time with no long term effects, however approximately 10% of horses may continue to demonstrate some neurological deficits.

Prevention and control of WNV

The best way to prevent WNV is through vaccination. The number of doses and timing of the vaccine to provide the best protection to your horse should be discussed with your veterinarian. In addition to appropriate vaccination, horse owners should limit mosquito exposure by removing stagnant water sources, ensuring water bowls are regularly cleaned and refilled, using approved mosquito repellants and keeping horses inside during peak mosquito times.

For more information

The Merck Veterinary Manual - WNV

Published date: 
October 12, 2018

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