If a horse becomes infected with EHV-1, clinical signs typically appear within five to 10 days, but that period may be prolonged 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 (incontinence) and decreased sensation in the tail and perineal area.

Less commonly, the horse may show symptoms related to the brain, such as neurologic facial signs and head tilt.

Other non-neurologic signs of EHV-1 may include nasal discharge, coughing and pregnancy loss in broodmares.

“Fever is the most consistent sign identified in EHV-1 infections, but it is usually not persistent,” Janke said. “It can come and go throughout the day, so owners should conduct temperature readings at least twice daily.

“The most concerning signs to watch for include fever, lethargy, limb incoordination, weakness, weak tail tone and urine dribbling,” he said. “These signs can progress to an inability to stand, known as recumbency.”

3. Diagnosis and reporting are key

If a horse is showing signs of EHV-1, its owner should contact a veterinarian as soon as possible to discuss diagnosis, treatment and quarantine.

“Any signs of fever along with hindlimb loss of coordination, urine dribbling or weak tail tone should prompt an owner to isolate the horse, stop the movement of any animals in contact, and reach out to their veterinarian immediately,” Janke said. “Your veterinarian will help ensure that the proper diagnostic tests are performed and will notify their state’s animal health official of the ongoing situation.”

The virus can be diagnosed with a nasal swab and blood test that is sent to a veterinary diagnostic laboratory. Results are typically available in as little as one to two days.

Because the virus has high outbreak potential, the veterinarian will advise quarantining sick horses until diagnostic results are available.

“Owners must recognize that EHM is a reportable disease because of its highly contagious nature and the serious effects outbreaks can have on the horse industry,” Janke said. “Therefore, owners need to follow their veterinarian's advice and the guidance of state animal health officials.”

4. Treatment focuses on managing symptoms

A horse infected with EHV-1 will be quarantined based on the guidance of state animal health officials. This may include confinement at home or, if symptoms progress, receiving pre-approval to transport the horse to a veterinary facility equipped to isolate and manage EHV-1 infections.

Supportive care remains the primary approach for treating EHM, so infected horses are often given therapies like intravenous fluids and anti-inflammatory medications.

Antiviral medications are commonly considered; however, there remains a significant lack of solid evidence that they are beneficial, according to Janke.

“When these medications are used, they appear to be most beneficial when initiated before clinical signs or at very early stages of disease,” he said.

Unfortunately, once a horse loses its ability to stand, the condition becomes much more difficult to treat.

“The prognosis for horses with EHV-1 infections varies widely; however, most outbreaks of EHM have an overall 70%-80% survival rate,” Janke said. “Horses with EHM that can still stand and show only mild to moderate neurologic signs have a good chance of recovery.”

An infected horse may continue shedding the virus even after symptoms are resolved, so it’s important to follow the guidance of your veterinarian and animal health officials. Repeated testing may be necessary before the horse is released from quarantine.

5. Prevention is the best protection

Although EHV-1 vaccines are widely available, it is important to recognize that no current vaccine option directly prevents the clinical signs of EHV-1 infections, particularly EHM.

“The benefit of vaccination is that immunized horses may shed less virus, resulting in less contamination of the environment and other horses,” Janke said. “Your veterinarian can guide you on the selection of appropriate vaccine products for your horses.”

The best form of prevention remains keeping healthy horses away from infected horses and any equipment or people that have come into contact with EHV-1.

If there is an EHV-1 outbreak in your area, avoid traveling with horses until the outbreak is resolved and your local animal health officials have announced that it is safe to travel in the area.

Finally, if a horse is suspected to be sick or has been exposed to EHV-1, begin taking twice-daily rectal temperature readings and immediately separate it from other horses. Monitoring rectal temperatures throughout an outbreak event helps owners identify infected horses early.

“Contact your veterinarian as soon as possible if your horse has been in contact with or is suspected to have been exposed to an infected horse,” Janke said. “This gives you a better chance of intervening early before clinical signs have developed. Your veterinarian can evaluate your horse's risk of developing the disease and, in some cases, may prescribe preventive medications.”

In the event of an EHV-1 outbreak, the best steps an owner can take are closely monitoring their horses and acting immediately if infection is suspected. Simple precautions can make a big difference in stopping an EHV-1 outbreak in its tracks.

Editor’s note: Article provided by Texas A&M University College of Veterinary Medicine and Biomedical Sciences. [Lead photo by georgeclerk from Getty Images.]

Angus Beef Bulletin EXTRA, Vol. 17, No. 12-A