West Nile Virus in Horses

West Nile is a mosquito-borne virus that attacks the brain and spinal cord. There is no cure once a horse shows signs — but it is one of the most preventable diseases we deal with, because the vaccine works.

Call 918-486-VETS Hours & location

Point Blank Range winning the 2026 Heritage Place Derby (G2)

Preventable.
Mostly.

A mosquito disease, in a state full of mosquitoes.

Birds carry the virus; mosquitoes move it from birds to horses. Horses are dead-end hosts — an infected horse can’t pass it to people or to the horse in the next stall. Oklahoma’s long, hot mosquito season, and standing water after summer rains, give the virus a long runway here, with cases clustering in late summer and fall. Diagnosis is by blood test, and there is no antiviral cure — treatment is supportive care while the virus runs its course. Everything about this disease points the same direction: vaccinate.

Signs of West Nile infection

Fever and depression: Often the first signs — a horse that’s dull, off feed, and running a temperature in mosquito season deserves a call, not a shrug.
Loss of coordination: Stumbling, incoordination, hind-end weakness, or going down and struggling to rise. The virus inflames the brain and spinal cord, and the legs show it.
Muscle tremors and facial changes: Fine trembling, a drooping lip or ear, a head tilt, teeth grinding, or trouble swallowing.
How it ends: Roughly one in three horses that develop signs dies or has to be euthanized, and survivors can be left with lasting deficits. That arithmetic is why prevention matters so much.

The vaccine schedule

A core vaccine: West Nile vaccination is core — recommended for every horse, every year, whether the horse ever leaves the farm or not. The mosquito comes to the horse.
Starting out: An unvaccinated horse, or one with an unknown history, needs a series: two doses, three to six weeks apart, before it’s protected. A single shot in a never-vaccinated horse is not enough.
Foals: Foals start the series at about four to six months of age, with doses spaced as directed, then join the annual schedule.
Broodmares: Broodmares are boosted four to six weeks before foaling, so the foal picks up protection through the colostrum.
Annual booster — timed to mosquitoes: The yearly booster goes on in spring, ahead of mosquito season, so protection peaks when exposure does.

Why fall boosters matter in Oklahoma

Our season runs long: In much of the country, one spring booster covers the season. Oklahoma mosquitoes can stay active into the fall, and vaccine protection wanes over the months — for horses at higher risk, a fall booster keeps coverage in place through the heaviest late-season exposure.
Who’s at higher risk: Horses on low, wet ground or near standing water; younger and older horses; and any horse whose last booster is already six or more months behind it when fall arrives.
Barn-side prevention, too: Dump and drain standing water, keep fans on stalled horses — mosquitoes are weak fliers — and consider dusk-to-dawn stabling at peak season. Vaccination plus management beats either one alone.

West Nile virusCore vaccinesFall boostersMosquito seasonBroodmare boosters

Serving horse owners across northeastern Oklahoma — Coweta, Broken Arrow, Wagoner, Tulsa, Bixby, Jenks, Owasso, Claremore, Muskogee — and welcoming haul-in clients from Kansas, Missouri, Arkansas, and Texas.

When to call us.

Neurologic signs are a same-day call. Vaccine questions take thirty seconds.

A horse showing neurologic signs — stumbling, trembling, weakness, fever in mosquito season — is the same-day call, not the wait-until-morning call. And if you’re not sure your horse’s West Nile vaccination is current, that’s a short phone call now instead of a hard conversation later. West Nile is part of the core vaccine review built into our equine care program, and a fall booster rides the same visit as a fall exam, the same haul or farm call. Call (918) 486-8387 and we’ll check your horse’s record against the calendar.