Going viral: the equine herpesvirus outbreak and Michigan's disease reporting tools
No reported cases in Michigan as of this weekend, as some horses were set to leave their quarantine
Originally published Dec. 8, 2025
LANSING — As news spread about an outbreak of equine herpesvirus-1 at events out west, the Michigan Department of Agriculture reached some owners of at-risk horses before they even made it home from Oklahoma.
The Barrel Futurities of America World Championships in Guthrie, Oklahoma, was scheduled for Sunday, Nov. 16, through Friday, Nov. 21. By Tuesday, Nov. 18, the event was called off after a horse there was diagnosed with EHV-1.
Karen Hopper Usher
Earlier reporting
The Michigan Hoof Beat spoke with six owners (or competitors) from Michigan, all of whom said their horses were on the road by the next morning. Many said they drove straight through because making a layover stop would have put other horses at risk of the highly contagious disease.
The outbreak of EHV-1, which experts this week called an epidemic because the outbreak was considered “uncontrolled,” is linked to an event in Texas that closely preceded the BFA event, with some horses attending both.
The Women’s Professional Rodeo Association (WPRA) World Finals and Elite Barrel Race event was held in Waco, Texas, Nov. 5-9. As of early Sunday morning (Dec. 7), 60 positive EHV-1 tests were linked to the WPRA event; 47 of the horses that tested positive for EHV-1 had Equine Herpesvirus Myeloencephalopathy (EHM), the neurologic form of the disease, according to the Equine Disease Communication Center.
None of the horses with positive test results were from Michigan, and the state said this week that, as far as the state knows, none of the horses that were at the BFA event had shown symptoms, and all were in quarantine at the time of the press release (Tuesday, Dec. 2).
In some cases, owners with whom The Michigan Hoof Beat spoke said their horses would likely be leaving quarantine over the weekend, as the guidelines typically say to quarantine for 14 days post-exposure to EHV-1 if the horse never shows symptoms.
It can take longer for symptoms to appear; there have been instances of horses showing symptoms 21 days after exposure.
If the horse does get sick and develops EHM, the American Association of Equine Practitioners guidelines call for the horse to be isolated immediately, with the facility premises quarantined for a minimum of 28 days. During the 28-day period, the horses should have their temperatures checked twice daily, and monitored for signs of EHV-1. If a new horse gets sick, the countdown re-starts.
“In some cases, state animal health officials may allow horses to be released from quarantine/isolation prior to 28 days from the last detected fever. EHV-1 testing (by qPCR) of horses considered exposed or infected would allow for increased confidence in the release of restrictions/isolation prior to the 28-day time period,” states AAEP’s guidelines, published in 2021. “All quarantine decisions should be in compliance with requirements by state animal health officials for the duration of quarantine and testing.”
An Equine Disease Communication Center disease alert entry about the outbreak, dated Dec. 4, said there had been 30 horses with neurological symptoms reported in Texas to date, and five of the horses died or were euthanized.
EHV-1 symptoms, monitoring and prevention
Disinfection and social isolation are essential tools for limiting the spread of EHV-1.
Most of the time, if the horse has symptoms of EHV-1, they’re respiratory and might include fever, lethargy, nasal discharge, and coughing.
But sometimes the virus takes a neurological form, EHM, with signs such as stumbling, hind-end weakness, going down and struggling to rise, and a distinctive “dog sit” position.
(See more a extensive list of symptoms at the AAEP’s Equine Herpesvirus (EHV-1 & EHV-4) Disease Guidelines).
EHM is fatal for 10-30% of horses, vets said during a United States Equine Federation webinar last Monday afternoon.
Other times, if EHV-1 spreads through a herd of broodmares, it can cause a so-called “abortion storm.”
USEF hosted a webinar on EHV-1 and biosecurity, Dec. 1, 2025.
EHV-1 is widespread throughout the horse population, though it is usually latent.
“Clinicians should presume that most horses are latently infected with EHV-1. Subclinical shedding of EHV-1 is relatively infrequent,” states a 2024 update to the American College of Veterinary Internal Medicine (ACVIM) consensus statement on EHV-1.
In the past few weeks, some experts have said as many as 40 percent of horses may have latent EHV-1; they have been infected with the virus but it’s not causing symptoms. However, the above consensus statement calls that figure into question.
“Although many authorities suggest the prevalence of latent EHV-1 infection in adult horses to be in excess of 60%, four-to-six more recent publications have estimated that the percentage of latently infected horses is much smaller and ranges from 15% to 27%,” reads the statement.
Stress, such as travel, can provoke the latent virus, causing symptoms and making it more likely the infected horse will spread the virus.
It’s difficult to predict which horses will develop neurological symptoms rather than the more common respiratory symptoms.
“The factors that lead to development of EHM are poorly understood, but in experimental infection studies, it occurs at much higher rates in old horses (18 years+),” the consensus statement read. Researchers are investigating certain strains, but “currently, it is not clear that any specific EHV-1 strain is more likely to cause neurological disease.”
All the competitors The Michigan Hoof Beat spoke with said they kept their horses at home rather than at a boarding facility. They quarantined the potentially exposed horses from the rest of their herds using methods such as an indoor arena, pens, or back pastures.
Experts have stressed the importance of cleaning and then sanitizing gear and have reminded horse owners not to allow horses to touch noses, and to limit the sharing of equipment between horses.
BFA competitors in Michigan with whom the Hoof Beat spoke discussed using separate gear and changing clothes when handling the isolated horses on their farm. It can be a big job, particularly when the isolated horses are in a back pasture far from the barn’s infrastructure, as is the case with one Upper Peninsula horse owner.
“It just sucks for me, because I got to feed the horses in the barn, first . . . then I go back in and I change my clothes, and I get into different clothes, and then I go out,” explains Jerri Hoholik of Manistique. She uses her side-by-side vehicle to haul hay to her isolated horses. “But see, it's so far out, I don't have a way to keep the water from freezing, so I'm out there three times a day making sure they got fresh water . . . This is real pain in the butt, but I definitely didn't want any horses to get it.”
Interstate communication about Michigan barrel racers
It was not clear by this weekend exactly how many horses from Michigan attended the events in Oklahoma and Texas. The WPRA and the Texas Department of Agriculture did not respond to an email (Thursday and Friday, and Friday, respectively).
The BFA and the Oklahoma Department of Agriculture responded to some questions, but did not say precisely how many horses from Michigan attended the event.
In an email, Rod Hall, DVM, state veterinarian in Oklahoma, said all state veterinarians are members of the National Association of State Animal Health Officials (NASAHO).
“We all know each other and communicate as a group and individually regularly,” Hall said.
“After we obtained the list of competitors from the BFA event, we sorted it based on the state of origin of the horse and sent the State Veterinarian’s office in that state a list of horses and competitors that entered the event from their state,” Hall wrote. “Michigan was one of 28 states we had on the list, and we sent (Dr. Nora Wineland, Michigan state veterinarian)’s office the list of Michigan horses that entered the event.”
A Michigan Department of Agriculture spokesperson said MDARD called horse owners from the event after receiving the list, ensuring “they were aware of the potential exposure and they know what to look for when monitoring horses.”
Between four BFA Finals entry lists dated Oct. 21 that were readily available online, there were seven owners from Michigan. The Michigan Hoof Beat spoke with five of them. Social media pages from the other two indicated that the owners had quarantined their horses and the animals had recently tested negative for EHV-1.
An eighth person, Terri Langworthy of Sturgis, wasn’t on the list; she rode an out-of-state friend’s horse.
Langworthy’s own horses were safe at home, she told The Michigan Hoof Beat. But the competition ended early, and by Wednesday morning, Langworthy’s friend’s horses were on their way home to Indiana.
Langworthy herself stayed behind in Oklahoma for a few extra days, cleaning and disinfecting anything that touched a horse so she wouldn’t inadvertently bring the virus home on her gear.
Social media reacts to EHV-1 outbreak
Ask Karen Waite Warner about the ongoing equine herpes outbreak, and she says she’s never seen anything like it. But she’s not talking about the disease itself. She’s talking about you. About us. About our collective response to a virus that was first identified in 1882 and has been threatening horses and the industries that rely on them ever since.
“It is a social media firestorm unlike anything I have really ever seen as it relates to equine-related things,” she said.
Warner is the Director of Undergraduate Education in the Department of Animal Science at Michigan State University and coordinates the equine industry concentration in the department. This fall, she’s teaching Intro to Horse Management, during which she covers equine herpesvirus-1 (EHV-1) and strangles (Streptococcus equi).
Warner spoke to The Michigan Hoof Beat shortly after news of the EHV-1 outbreak began circulating.
Every expert with whom The Michigan Hoof Beat spoke, including Warner, said the Equine Disease Communication Center has the most current data on the spread of the EHV-1; the state of Michigan also encourages horse owners to use the EDCC as a resource.
However, there are gaps in information available to the public.
The EHV-1 cases posted to the EDCC dashboard are only those in which a horse has tested positive for the herpesvirus.
“It's voluntary to be reported to the EDCC. It's not voluntary to be reported to the state animal health official and state vet,” said Nat White, DVM, DACVS, Director of the Equine Disease Communication Center.
In Michigan, EHV-1 is a reportable disease; veterinarians and owners are supposed to notify the state even if the disease is only suspected. But the dashboard shows the general public EHV-1 cases only after a lab confirms the disease is present.
The owner’s information is not subject to Freedom of Information Act requests, according to the Michigan statute regulating reportable animal disease.
Historically, farm owners have been reticent to share information about infectious disease on their farms.
“One of the things we've had to overcome is the fear of a particular farm or stable or event place being noted in one of our alerts,” White said.
White praised Michigan for sharing reports with the EDCC, calling the state a model for others because it readily shares information about reportable equine diseases with the EDCC.
According to the MDARD Companion Animal, Exotic Animal, and Equine Reportable Disease Dashboard, the last EHV-1 or EHM case in Michigan was in September of 2024; before that, it was in 2022.
Michigan Animal Disease Dashboard
There was an outbreak tied to a racetrack in Michigan about a decade ago, Warner recalled.
Because the horse industry can be segregated by discipline, when an outbreak happens in one horse-related community, other horse-related communities were known to “act like nothing’s going on,” Warner recalled.
This time around, however, the human element has just survived the COVID-19 pandemic. Talk of quarantines, event cancellation, respiratory disease and vaccination draw emotional responses. People from disparate disciplines have publicly discussed cancelling events or closing facilities to haul-in usage.
Emily Golden, of South Boardman, works as an emergency room nurse and took three horses with her to Oklahoma. She estimated that she was on the phone with her vet for an hour and a half while she drove her rig home.
Golden says she’s seen nasty comments online, with people calling competitors selfish or criticizing the BFA. For her part, Golden says she felt like the organization handled the situation well, and said competitors didn’t know they were exposing their horses to EHV-1.
“Now that we do know—like everybody, don't panic and run—like, we have to deal with it and move on,” said Golden, who pointed out that the EHV-1 virus is old and has always been around.
Golden’s sentiments were similar to those expressed by Warner.
“I don’t think there’s cause for complete panic,” Warner said. “We have had outbreaks like this before.”
Warner went on to clarify that her answer might change if Michigan were to develop a positive EHV-1 case.
The Michigan Hoof Beat asked Golden and the other barrel racers what they want horse owners in Michigan to know about their response to the EHV-1 outbreak.
“I do think people even up here (in Michigan) did their part,” by shutting things down and staying home, Golden said. She’s not expecting the EHV-1 to spread in Michigan.
“I think the risk is pretty low,” Golden said. “I mean, it can happen—not saying it can't happen—but, you know, nobody wants to go anywhere right now. It's like 25 degrees outside.”
"The EDCC relies on the support and generosity from donations to provide critical infectious disease information. Supporters (Sponsors) of the EDCC understand the value in having a universal communication system to coordinate responses to infectious diseases. Not only does EDCC provide up-to-date disease alerts in North America, the EDCC website has a wealth of information about diseases and what owners and veterinarians can do to prevent and mitigate disease outbreaks."
Publisher's note: The Michigan Hoof Beat, in alignment with the newsletter's editorial policy regarding health and science news, allowed Nat White of the EDCC and Karen Waite Warner of Michigan State University to review the article before publication.
