Mosquitos Are Coming

West Nile Awareness

by sagebrushwriter – June 1, 2012

Mosquito season is almost upon us. More than just being annoying, mosquitos can pose a serious risk to horses because of their potential to transmit West Nile Virus. The Nevada Department of Agriculture has been tracking cases of West Nile since it was first diagnosed in the state in 2004. They logged eight equine cases in 2017 and the same number in 2016.

Horses are infected by West Nile through the bite of mosquitos. The virus is not contagious between horses or from horse to human, but it can be deadly for the infected horse. There is no treatment for West Nile, so it is critical that horse owners take steps to reduce their horse’s exposure to mosquitos and know the symptoms of infection.

Signs and Symptoms

West Nile is a neurological disease that attacks the horse’s nervous system, mainly the spinal cord. Owners should be alert for quivering in the horse’s skin around the nose, mouth, and shoulder, but a major sign of West Nile infection is a horse that is down and cannot get up. “It attacks the hindquarters first because of the way the nerves are arranged in the spinal cord,” says Susan McCartney, a doctor of veterinary medicine who practices in northern Nevada. “You might see a horse dragging its hind legs or weakness in the rear quarters and then it progresses to them being down and unable to get up at all.”

Dr. McCartney says West Nile can be confused with other neurological diseases or some arthritic conditions. The only way to diagnose West Nile is to take a blood sample. But by then, it may be too late. “A lot of them that I’ve seen can’t even lift their heads to eat and drink so at that point we euthanize them,” says Dr. McCartney.


The best way to protect your horse from West Nile is to vaccinate against it. “The data that I’ve seen says that the vaccine is about 96% effective, which is very good for any vaccine,” says Dr. McCartney. Vaccinations should be given annually each spring, before mosquito season gets underway. In addition to vaccinations, horse owners can also reduce exposure to mosquitos by using insect repellent, eliminating standing water where mosquitos can breed, and by regularly cleaning water troughs.

These habits will also protect humans, who can also be infected with West Nile. Call your vet immediately if you suspect your horse is showing symptoms of West Nile.

Learn More

You can monitor West Nile reports in the state through the Nevada Department of
Agriculture website: