Equine virus detected in PA unrelated to Waco outbreak

11/28/25

By Lauren Royce, Editor

PENNSYLVANIA — A mildly fatal respiratory disease in horses is spreading across multiple states after a championship rodeo event in Waco, Texas, earlier this month. The Pennsylvania Equine Council (PEC), Equine Disease Communication Center (EDCC) and Pennsylvania Department of Agriculture (PDA) are advising horse owners to take precautions and avoid traveling too much in and between states.

As of Nov. 27, the EDCC and Dept. of Ag said two confirmed cases unrelated to the Texas outbreak were recorded in Pennsylvania, on a farm in Lancaster County. A third horse was suspected of having it and one horse was euthanized.
Multiple equine events have been put on hold or cut back until further notice, including events at the Pennsylvania Farm Show in Harrisburg the weekend after Thanksgiving.
The disease, Equine Herpesvirus Myeloencephalopathy (EHM) is highly contagious, with a fatality rate of around 30-50% according to the EDCC. Transferred by coughs and sneezes, it is easy for equipment to be contaminated.
“The Equine Disease Communication Center is monitoring an outbreak of EHM that originated at the Women’s Professional Rodeo Association (WPRA) World Finals and Elite Barrel Race event Nov 5-9,” reads a statement on the EDCC website. “To date, officially confirmed cases have been reported in the following states: Texas, Oklahoma, Louisiana, South Dakota, Colorado, New Mexico, Arizona and Washington.” As of Nov. 23, at least one horse had died in Texas.

“Horses carry this all the time, it just surfaces whenever they’re stressed,” said Capri Stiles, president of the Pennsylvania Equine Council and biosecurity educator for Pennsylvania 4H.
“Right now is a big time of year when we’re pulling our horses in off the pasture, so not only are their digestive systems stressed a little but with the change in diet, the weather’s changing and the conditions are right for the disease to become a little bit more virulent.”
“What’s unique about this time is that it was a world class event, so there were people there from probably all 50 states and Canada,” Stiles said. “And once they discovered that’s what was going on with this horse, some people had already left to travel home. That event is oftentimes a culminating event and that’ll be the end of the season, and then that horse is going home to rest for the rest of the winter, especially around here.”
Stiles said veterinarians and state agencies are not required to report to the EDCC, but they are required to let the state veterinarians know of cases and suspected cases. There was one case of EHV-1, not EHM, in Northumberland County, and it was not associated with the outbreak from Waco, Texas.
Stiles said she estimated that roughly 659 entries made up the events in Texas, based on numbers pulled from rodeos that participated in the event.
“There were definitely horses from Pennsylvania, a lot of them are from Pennsylvania but they opted to just keep the horses down there until the quarantine’s over,” Stiles said. “Some horses did come back— through the Certified Veterinary Inspection (CVI), the Pennsylvania Department of Agriculture was able to track those people and get in touch with them and let them know that they are under strict quarantine orders to keep that horse separate from other equids at this time.”

Stiles said that similar to how disease operates in people, a horse’s resilience to EHM depends on how they are kept, either mostly inside or outside of a barn.
“Limit human (foot) traffic,” Stiles said. “Humans are one of the big carriers, so you want to limit who comes and goes from your farm. If you have a horse for sale, please either hand them booties to put on or ask them to wear a pair of shoes that they have not worn around any other horses for at least three days and have been disinfected.”
Quarantined horses should have separate feed and feeding equipment, and should be fed after the healthy horses. Despite it being tempting to feed them first, Stiles said it’s important to be mindful of cross contamination.

If owners suspect a horse has EHM, Stiles said they should contact their regular vet. Vets from the PDA do not charge to come out to your farm for disease mitigation. Isolate the horse(s) 150-200 feet from other horses and take temperatures twice daily if you have had horses off the farm since the beginning of November. If hauling a horse is necessary, check your state’s restrictions on interstate and intrastate travel.
“The neurologic piece of that is when it mutates into EHM, which enters the spinal cord and causes mostly hind-end neurologic issues,” Stiles said. “If they show neurologic symptoms, the more severe they are, the less likely it is that they will completely recover and return to work.”
Now is the end of the “first wave,” the 21-day window from the first horse being diagnosed. The second wave is when the next set of horses reach the incubation period and then get sick, so on and so forth.

There is no cure currently for EHM. There are vaccines for EHV-1 and EHV-4 strains of Equine Herpesvirus. Stiles said that how EHM jumps to affect the spinal cord is something still being studied and the best thing owners can do is supportive care, with electrolytes and helping the horse stay strong enough to fight the disease. Sunlight is effective in making it harder for pathogens to live and spread, but dark and damp weather at this time of year create conditions that make it easier for them to thrive, she said.
As the biosecurity educator for PA 4H, Stiles teaches youth and 4H families how to create biosecurity plans and how to address diseases like EHM to keep their animals safe. With the PEC, she helps people learn more about horses and how to take care of them. That, and how to navigate the line of separation in a display of a quarantine area.
“We (the PEC) go to the Pennsylvania Farm show, and we have about five horses that come for kids to pet,” Stiles said. “Last year our estimate was 54,000 people engaged with a horse at the farm show. It’s called the equine learning center— we’re not sure that we will be able to do that this year.” The Pennsylvania Farm Show is currently scheduled for Jan. 10-17 in Harrisburg. Stiles expected the PEC to make a decision on what to do by mid-December.
Stiles said this disease requires very strict parameters when it comes to containment and quarantine. Barns need to have a designated quarantine zone that does not cross contaminate with other areas. Boots that go over the contamination line must not touch back on the other side.
“It literally is a line where you do not want any contact with fomites, which are any kind of inanimate object that can transfer the pathogens– from one side to the next.”
While the disease does not affect any animal besides equids, it can jump onto clothing items, tack, onto dogs’ foot pads and into their nasal cavities, making them a prime spreading agent.
Because of this, Stiles said she recommends people not bring their dogs out to horsing events.
Certain disinfectants such as Novalsan, which contains chlorhexidine, can diminish effects of EHM if people want to wash their pets’ feet.

Stiles said the most recent EHM outbreak she could recall happened a few years ago, in Washington County at The Meadows Racetrack & Casino. A report by Tribune-Review said it was 2018 when 190 horses had been quarantined at the facility because of the event. There were a few isolated cases of the disease last year, but nothing to the current scale.

Stiles said horse owners responding accordingly should not be seen as panicking, but being proactive and adamant in their animal care.
“It should be a cultural shift at this point, because we’re seeing some pretty nasty diseases throughout the farming community,” Stiles said. “It’s just one of those things where we would like to see the entire farming community have a dedicated pair of footwear that they use only around their farm, and then whenever they go to other places, they should have a different set of footwear.”
Shannon Powers, Press Secretary of the Pennsylvania Department of Agriculture responded to email questions Wednesday with the following statement:
“On Wednesday, November 19, Pennsylvania Department of Agriculture veterinarians learned of a multi-state outbreak of Equine Herpesvirus Myeloencephalopathy (EHM). EHM is a highly contagious, sometimes fatal neurological disease of horses. Horses whose owners were located in 31 states and Canada were exposed to the virus during rodeo events in Oklahoma and Texas earlier this month. Pennsylvania’s state veterinarians have been working with state, federal, and private veterinarians nationwide to trace exposures and current locations of Pennsylvania horses. State veterinarians have notified horse owners, trainers, veterinarians, equine event managers, fairs, racetracks, and other related organizations statewide.
There have been no reported cases of EHM in Pennsylvania tied to this outbreak. Four horses confirmed to live in Pennsylvania were exposed at the event. These horses have been under quarantine out of state. None have shown signs of the disease. They will continue to be quarantined on their return to Pennsylvania.
A horse diagnosed with Equine Herpesvirus (EHV) in early November in Northumberland County is not linked to the outbreak at recent rodeo events. The horse was diagnosed with EHV4, a milder form of the virus that is a fairly common respiratory illness among horses. EHV4 generally does not produce neurological disease.
The organizers of Bull Ride Mania events held at the Pennsylvania Farm Show Complex over the November 21-23 weekend chose to cancel some events that involved horses from other states. Other events continued as scheduled, with only Pennsylvania horses that have not been exposed to the virus.
If a horse tests positive for EHV and has neurologic signs, the diagnosis is EHM, and the horse is quarantined and given supportive care.
While EHM is a serious disease, the majority of cases are not fatal. Veterinary evaluation and isolation of exposed or affected horses is crucial.
Viruses like EHV can be transported on equipment, clothing, boots, and other items used around animals. Good biosecurity can prevent transmission if implemented consistently.
Horse owners are advised to carefully monitor their animals for signs of the disease. Signs of EHM include:
Fever, which may be intermittent throughout the course of disease. The absence of fever does not rule out EHM. Nasal discharge, lethargy, swollen lower limbs, incoordination, hind limb weakness, urine dribbling or inability to urinate, sitting in a dog-style position, leaning against a fence or wall to maintain balance and inability to rise. EHM does not affect humans.
Horse owners are encouraged to visit the Equine Disease Communications Center for up-to-date information on this outbreak, as well as information to protect your horses. Veterinarians are required by Pennsylvania and federal law to report any suspected cases of EHM to the Department of Agriculture at 717-772-2852.”