EHV-1 outbreak prompts urgent response

A recent multi-state outbreak of equine herpesvirus-1 (EHV-1) and its neurologic form – equine herpes myeloencephalopathy (EHM) – has halted major equestrian events across the U.S. during one of the busiest months on the Western performance horse calendar.

While there have been no cases confirmed in the state of Wyoming as of Nov. 25, state officials are tracking potential exposures connected to horses which recently traveled to events in Texas, Oklahoma, Colorado and Wyoming.

The outbreak, which emerged after several large Western-performance horse gatherings – including the
Women’s Professional Rodeo Association (WPRA) World Championship Barrel Racing Finals in Waco, Texas – has already resulted in confirmed EHM cases and equine deaths in Texas and Oklahoma. 

Because horses can shed the virus before showing symptoms, nationwide efforts are being made to take aggressive precautions.

Signs and symptoms

According to Dr. Jared Janke, a clinical associate professor of equine internal medicine in Texas A&M University’s College of Veterinary Medicine and Biomedical Sciences, EHV-1 is a highly contagious equine virus, which is easily spread via direct contact; in aerosol droplets up to 30 feet; on shared tack, stalls, buckets and trailers and on handlers’ hands, clothing and equipment. 

Symptoms of EHV-1 and EHM include fever, nasal discharge, cough, incoordination, hind-limb weakness, urinary dribbling, pregnancy loss in broodmares and, in severe cases, the inability to stand up. 

Janke notes clinical signs of EHV-1 will usually appear within five to 10 days or even longer in cases of EHM. 

“EHM signs, caused by damage to blood vessels in the spinal cord and brain, often include high fever, lack of coordination, weakness, urinary dribbling and decreased sensation in the tail and perineal area,” Janke explains in a Nov. 21 Texas A&M University Newswire article. “Less commonly, the horse may show symptoms related to the brain, such as neurologic facial signs and head tilt.”

While fever is the most consistent sign of EHV-1, Janke notes it usually isn’t persistent and may come and go throughout the day, meaning individuals should check their horses’ temperatures at least twice a day. 

He also points out some infected horses never show outward signs but still shed the virus.

Prevention and treatment

If a horse does exhibit signs of EHV-1, officials encourage owners to contact a veterinarian as soon as possible to help with diagnosis and treatment. 

Diagnosis can occur by sending a nasal swab and blood test to a veterinary diagnostic lab, in which results are typically available in one to two days. 

Since the virus has such high outbreak potential, state animal health officials require animals to be quarantined.

According to Janke, supportive care remains the primary approach to treating the virus, so infected horses are usually given intravenous fluids and anti-inflammatory and/or antiviral medications. 

“When these medications are used, they appear to be most beneficial when initiated before clinical signs or at very early stages of disease,” Janke says. “Unfortunately, once a horse loses its ability to stand, the condition becomes much more difficult to treat.”

Although EHV-1 vaccines do exist, Janke points out no current option on the market directly prevents clinical signs of the virus, and he notes the best form of prevention includes keeping healthy horses away from infected horses. 

Exposure and response

In a Nov. 20 press release, the Wyoming Livestock Board (WLSB) confirms no horses in the state of Wyoming have tested positive for EHV-1 or EHM.  

However, a single horse traveling from the WPRA event in Waco, Texas which later attended shows in Cheyenne on Nov. 15 and Wheatland on Nov. 16 later tested positive for EHV-1 in Colorado, meaning there is potential horses in Wyoming could have been exposed. 

WLSB officials say they are prepared to issue immediate hold orders if trace contacts are confirmed. 

“This outbreak serves as a reminder of the potential disease risks associated with large equine events,” WLSB states. “It shows the importance of timely reporting of diseases and ensuring movement requirements are followed, such as veterinary inspection, health certificates and current Coggin’s tests prior to travel.”

For those who have attended a multi-state equine event in recent weeks, the agency recommends isolating horses for 21 days after last possible exposure; avoid sharing equipment, water sources and/or handlers; implementing strict barrier precautions; monitoring body temperature twice a day; paying close attention to respiratory or neurological signs and reporting any concerning symptoms to a veterinarian immediately. 

WLSB further suggests avoiding travel to commingled-equine events until the outbreak stabilizes and maintaining strict biosecurity measures at home and on the road. 

They also note horse owners should expect new health certificate windows and reminds them to follow individual state import requirements, as many will likely change temporarily at this time. 

Event organizers are urged to consult local veterinarians and consider postponement. 

If events continue, WLSB says they should require short-window health certificates, increase sanitation, limit barn-to-barn movement and provide temperature logs on entry.

Veterinarians must report acute neurologic disease to WLSB and submit paired samples – a nasal swab and whole blood sample – due to variable viral shedding.

Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.