As spring travel ramps up for horse shows and events, equine health experts are urging horse owners not to let their guard down against equine herpesvirus (EHV).
In November, the Equine Disease Communication Center (EDCC) monitored an outbreak of equine herpes myeloencephalopathy (EHM), the neurologic form of EHV-1, associated with a Women’s Professional Rodeo Association World Finals barrel-racing event held November 5-9 in Waco, Texas. Swift action within the equine industry helped limit the spread.
“The spread in the current outbreak was limited by rapid communications in the industry to owners and veterinarians by the EDCC,” Dr. Nathaniel A. White II, EDCC director, told AVMA News (avma.org). White added that EHV is easily spread by aerosol and contact and can become active with stress from transport or new environments such as horse shows.
Despite the successful containment of the outbreak, veterinarians stress that EHV remains a persistent risk.
“The Waco outbreak has ended, but EHV-1 cases and outbreaks occur intermittently in equine populations, particularly those that travel and show routinely,” said Dr. Kaitlin A. Mielnicki, assistant professor of large animal clinical skills at Oklahoma State University’s College of Veterinary Medicine. “Cases are more commonly diagnosed in the fall, winter and spring months. So it is especially important that while we may now feel safe, we must not let our guard down.”
As Oklahoma horse owners prepare for a busy spring season, staying informed and proactive remains one of the best ways to protect both individual horses and the broader equine community. In the accompanying article, Mielnicki outlines the key facts horse owners should understand about EHV-1 and practical biosecurity steps to minimize exposure during travel and competition.
Understanding Equine Herpesvirus
by Dr. Kaitlin Mielnicki
Equine herpesvirus is a family of nine viruses named by numbers.
EHV-1, the virus associated with the ongoing outbreak, is most commonly associated with respiratory tract infections. EHV-1 is also associated with neurologic disease and abortion. Upwards of 70% of horses are infected with EHV-1 as a youngster and carry it with them for the remainder of their lives.
Respiratory illness caused by EHV-1 often presents with fever, clear nasal discharge and coughing. Horses will spread the virus before they actually show outward signs that they are sick. Pregnant mares may experience sudden late-term abortion of the fetus. In some horses, the virus progresses to equine herpes myeloencephalopathy (EHM), causing incoordination, hind-limb weakness, reduced tail strength, dribbling urine or sudden inability to stand. Commercial vaccines are available for EHV-1 and -4. While vaccination for EHV is known to be beneficial in reducing respiratory and reproductive disease, it cannot protect a horse from developing neurological symptoms.
Equine herpesvirus is spread from horse to horse through nasal discharge, aerosolized droplets from coughing, and contact with contaminated surfaces. People can also inadvertently spread the virus between horses on their hands, clothing or equipment, though humans themselves cannot contract the disease.
Veterinarians advise that any horse showing signs of illness should be isolated from all other horses immediately, and owners should contact their local veterinarian immediately, as swift assessment of possible exposure(s) and strict quarantine procedures are essential in stopping further spread of the virus.
Such health and safety methods might include the following measures:
- Monitor rectal temperatures twice daily for all horses that may have been exposed. A normal temperature ranges from 99.0 F to 101.5 F. Any elevation in temperature may indicate early infection. Note: The use of non-steroidal anti-inflammatory drugs, such as phenylbutazone (“Bute”), flunixin meglumine (“Banamine”) or firocoxib (“Equioxx”) can mask a fever. Recheck your horse’s temperature 12-24 hours after the last dose of any of these medications.
- Restrict movement on and off their property.
- Follow strict biosecurity protocols.
- Maintain thorough notes on symptoms and changes in behavior.
Close collaboration with a veterinarian is critical for determining appropriate testing, treatment and monitoring. Proper EHV testing plays a significant role in confirming cases. When collecting samples, you must obtain a deep nasal swab using an appropriate synthetic or flocked swab and a minimum of 2-5 milliliters of blood in an EDTA (purple-top) tube. Samples must be handled with care, kept cold but not frozen, and shipped overnight for timely processing. The Oklahoma Animal Disease Diagnostic Laboratory also accepts hand-delivered samples, including after-hours drop-off.
State officials and veterinarians continue to monitor the situation closely. Horses showing symptoms consistent with EHM must be reported to animal health officials to assist with assessment of the outbreak. While EHV remains a serious concern, early detection, proper isolation and strong biosecurity measures can significantly reduce the risk of widespread transmission. Horse owners are encouraged to stay informed through official state updates and to contact their veterinarian with any questions or concerns regarding symptoms, exposure or testing.
