West Nile Virus in Horses: 2026 Cases, Symptoms and How EEE Differs

West Nile virus in horses: what it is and why it's in the news

Update (2026-11-03): On Nov. 2, the EDCC posted a confirmed West Nile case in an unvaccinated 2-year-old Morgan filly in Grant County, Wisconsin, who is recovering. West Nile virus in horses is a mosquito-borne infection that can inflame the brain and spinal cord, causing muscle twitching, weakness and stumbling.

Horses can't pass it to people or to other horses, but roughly one in three horses that show signs dies. The same day, Florida reported a Columbia County horse that tested positive for both West Nile and EEE and was euthanized, a reminder that in the South the season isn't over in November.

The Wisconsin filly's signs began Oct. 8, a sign that even up north the risk can last well into fall. Both reports follow a September wave: between Sept. 16 and Sept. 21, equine West Nile cases were reported in at least 10 states, including Kentucky's first confirmed case of the year. This season, Michigan, Wisconsin and Florida have also confirmed horses with eastern equine encephalitis (EEE), a related mosquito-borne disease that is even deadlier.

The good news: both diseases are largely preventable with core vaccines and steady mosquito control. Here's what's happening, what the signs look like and what to ask your vet now.

The latest 2026 cases

These reports come from state animal health officials through the Equine Disease Communication Center (EDCC) and from local news. Together they show how widespread late-season risk is.

October and November: Wisconsin and Florida

• Wisconsin (Grant County), posted Nov. 2: An unvaccinated 2-year-old Morgan filly at a private facility began showing signs on Oct. 8, including loss of coordination in all four legs and muscle twitching in the head and neck. The case was confirmed Oct. 15, and she is recovering. The EDCC alert, based on a report from Wisconsin's Department of Agriculture, Trade and Consumer Protection, lists 35 horses exposed and no quarantine; West Nile doesn't spread from horse to horse.
• Florida (Columbia County), reported Nov. 2: One horse tested positive for both West Nile virus and EEE and was euthanized, according to the Florida Department of Agriculture and Consumer Services. The report doesn't give the horse's age, breed, vaccination status or when signs began.
• Florida (Suwannee County), confirmed Sept. 8: Florida's first equine West Nile case of 2026, according to the Florida Department of Agriculture and Consumer Services. The horse was euthanized. Florida's health department has since added West Nile horses in Okeechobee and Glades counties.

September: West Nile in at least 10 states

• Kentucky (Washington County): An unvaccinated 3-year-old Tennessee Walking Horse mare showed signs on Sept. 5, including poor appetite, dehydration, muscle twitching and a paralyzed lower lip. She tested positive Sept. 18 and was euthanized. It is Kentucky's first confirmed equine case of 2026.
• New York (St. Lawrence County): An unvaccinated mare began staggering on Sept. 3, then sat like a dog, could not rise and was euthanized.
• Arkansas (Garland County): A vaccinated Thoroughbred filly at a training facility developed fever, twitching, sensitivity to noise and coordination problems. She is recovering.
• Washington (Franklin County): A 2-year-old filly is recovering under veterinary care.
• Wyoming (Uinta County): One horse at a private facility tested positive.
• Texas Panhandle: Dimmitt Veterinary Clinic reported a positive horse tied to Parmer and Lamb counties.
• Sept. 18 roundup: New cases in Pennsylvania (three counties), Tennessee, Michigan (two unvaccinated horses) and California, where a vaccinated gelding in Amador County became the state's 14th case of the year. He is recovering.

EEE in Michigan, Wisconsin and Florida

By early September, Michigan had confirmed at least two horses with EEE this year, and both were euthanized. One, announced Aug. 31, was an under-vaccinated yearling Quarter Horse colt in Clare County. The other, announced Sept. 8, was an unvaccinated 18-month-old Quarter Horse filly in Roscommon County.

Michigan also confirmed a human EEE case in a Roscommon County resident this summer. On Sept. 9, Wisconsin's health department announced the state's first EEE activity of 2026: a horse in Portage County.

Florida has confirmed the most equine cases of the three. By early September it had seven horses with EEE this year. The seventh, in Washington County, was reported Sept. 3. Another, an under-vaccinated 16-year-old Quarter Horse gelding in Indian River County, showed signs in August, including stumbling, loss of coordination and extreme sleepiness, and was euthanized. An early EDCC report on Sept. 1 said he also tested positive for West Nile, but Florida's official counts list him as an EEE case only. As of Oct. 17, Florida's health department still counted seven horses with EEE and three with West Nile this year; the Columbia County horse was reported after that.

The pattern worth noticing

In the reports above that list vaccine status, every horse that was euthanized was unvaccinated or under-vaccinated, and the vaccinated horses were recovering. Some unvaccinated horses recover too, like the Wisconsin filly, so a missing vaccine doesn't decide the outcome on its own. The Columbia County report doesn't say whether that horse was vaccinated, so it can't be counted either way. That's a handful of cases, not a study, and vaccinated horses can still get sick. Still, it fits American Association of Equine Practitioners (AAEP) guidance that EEE deaths are lower in horses with previous vaccination, and it's a reminder of why the AAEP calls both vaccines core.

West Nile symptoms in horses: the neurologic signs to watch for

Early West Nile can look vague, like a horse that seems "off," dull or isn't finishing its feed. In horses that get sick, signs can build quickly, so small changes deserve a closer look.

Watch for:

• Fever, dullness or loss of appetite (the "flu-like" start)
• Muscle twitching, especially around the muzzle, face, neck or shoulders
• A droopy or paralyzed lower lip
• Unusual sensitivity to touch or sound, like jumping at normal barn noise
• Sleepiness, confusion or other changes in behavior
• Stumbling, hind-end weakness or walking forward uncontrollably
• Sitting like a dog, going down or being unable to get up

EEE can look similar at first but often adds head pressing, circling, blindness or seizures, and it moves much faster.

What to do if you see these signs

1. Call your veterinarian right away. Describe exactly what you see and treat it as an emergency.
2. Take the horse's temperature only if you can do it safely. Our health basics page covers normal vital signs.
3. Move the horse somewhere safe if it can walk steadily: a well-bedded stall or small pen away from fences, ditches and other horses.
4. Keep kids and bystanders back. A neurologic horse can stumble, lean or fall without warning.
5. Wear gloves and keep your hands out of the horse's mouth. Rabies can look similar, and your vet will want to rule it out.
6. Let your vet handle testing. EEE is a reportable disease, and state animal health officials track West Nile cases too.

There's no cure for West Nile. Treatment is supportive care from your veterinarian, which is exactly why prevention matters.

EEE vs West Nile in horses: how they differ

Both viruses cycle between wild birds and mosquitoes, and both reach horses and people through mosquito bites. Horses are "dead-end" hosts for both: they don't carry enough virus in their blood to infect another horse or you.

Survivors of either disease can have lasting problems. AAEP figures suggest around 40% of West Nile survivors still have gait or behavior problems six months later, and EEE survivors may keep permanent neurologic deficits.

Here's the practical takeaway: no single sign proves which virus a horse has, so it takes lab testing. A horse can even be infected with both at once, as the Columbia County horse in Florida was this year. That's one more reason to call your vet instead of waiting to see.

Why late-season mosquitoes still matter

It's easy to think mosquito season ends when school starts. In reality, these viruses spend the summer building up in birds and mosquitoes, so risk to horses often peaks in late summer and early fall, exactly what this September's case list shows.

In colder states, risk fades after a hard frost. Wisconsin's health department defines that as temperatures below 28°F for at least four straight hours. Until then, cases can still turn up: the Grant County filly in Wisconsin got sick in the second week of October.

The South is different. In Florida and the Gulf South, a hard frost may come late or not at all, and mosquito-borne cases are still being confirmed in November, as the Columbia County horse shows. University of Florida extension guidance notes that mosquitoes stay active year-round in Florida, so don't treat fall as the end of the season there.

Fall also creates new breeding spots: clogged gutters, tarps, old tires and buckets that fill with rain. Mosquitoes feed most at dusk and dawn, and warm fall evenings still give them plenty of time.

West Nile vaccine for horses: fall boosters and what to ask your vet

The AAEP lists West Nile and EEE as core vaccines, meaning they're standard care for every horse in North America. The usual plan is a yearly booster in spring before mosquito season, but the AAEP also says extra boosters can be warranted based on local risk.

That's where a fall booster can come in. For higher-risk horses, the AAEP notes that more frequent vaccination may be indicated, so ask your vet whether that applies to your horse and your area.

In Florida and the Gulf South, where mosquitoes can be active all year, some vets advise West Nile and EEE boosters about every six months instead of once a year. University of Florida extension guidance, for example, recommends vaccinating Southeastern horses against EEE more than once a year, and against West Nile once or twice a year. Your vet will set the schedule that fits your horse.

Key points to know:

• Protection isn't instant. A vaccine needs time to work, so don't wait until there's a case down the road.
• A never-vaccinated horse needs a starter series, not one shot. Your vet sets the schedule.
• Young and older horses are higher risk. The AAEP flags horses under 5 and over 15 as more susceptible. Several 2026 West Nile and EEE cases, including the Wisconsin filly, were in horses 3 or younger.
• Vaccinated horses can still get sick, as the Arkansas and California cases show, though both of those horses were recovering.

Questions to ask your vet:

• Is my horse up to date on West Nile and EEE, or overdue?
• Given our local mosquito season, would a fall booster help? If we live in the South, should my horse be on a twice-a-year schedule?
• My horse's vaccine history is unknown. What does it need?
• Should anything change before we travel, show or move barns?

For the rest of your yearly health routine, see our care guide.

Your fall mosquito checklist

Three habits do the most: vaccinate as your vet advises, empty standing water every week and stable horses at dusk and dawn. In the South, keep them up through November and beyond.

• Vaccinate on your vet's schedule, including any extra boosters advised for your region.
• Dump and scrub water buckets and small troughs at least once a week. For big stock tanks, ask your vet or local extension office about mosquito dunks or mosquito-eating fish.
• Clear standing water every week from tires, tarps, wheelbarrows, flowerpots and clogged gutters.
• Stable horses at dusk and dawn, the peak mosquito hours, instead of turning them out then.
• Run barn fans to keep air moving over stalls.
• Use an equine-labeled insect repellent and follow the label directions.
• Add physical barriers: fly sheets, fly masks and leg wraps.
• Protect yourself too. People catch West Nile and EEE from the same mosquitoes, so use repellent and long sleeves for evening chores.

What to watch next

• Until the first hard frost, and longer in the South: Northern reports should taper off as frosts arrive, though cases from October, like Wisconsin's, can still be posted weeks later. Florida and the Gulf South can keep confirming cases through November and beyond.
• Your state veterinarian and the EDCC: Both post confirmed cases, often with the county and the horse's vaccine status.
• Cases near you: If one pops up in your county, call your vet about boosters, especially for horses with spotty records.
• Your horse, every day: A quick daily check of appetite, attitude and how it walks catches neurologic changes early. Our safety page covers handling a horse that's acting strangely.

Outside the United States, mosquito seasons follow local weather, not the US calendar. Wherever you live, ask your vet when your area's risk window opens and closes.