How to keep horses safe from EHV |

How to keep horses safe from EHV

Russ Daly
SDSU Extension Veterinarian, State Public Health Veterinarian
The most common way for EHV-1 to spread is by direct horse-to-horse contact. This virus is shed from infected horses via the respiratory tract or through direct or indirect contact with an infected aborted fetus and fetal membranes. Horses may appear to be perfectly healthy yet spread the virus via the secretions from their nostrils. Image courtesy USDA

In recent weeks, equine herpesvirus (EHV) infections have affected horses in South Dakota and the surrounding region.

These horses have been associated with travel to and from events such as rodeos where they have contact with numerous horses from a wide area.

While in general, herpesvirus infections in horses are not rare, this particular strain of the virus (the “neurologic” form) can cause severe and even fatal illnesses in those affected – this illness is sometimes referred to as “equine herpesvirus myeloencephalopathy” or EHM.

Like the other strains, the neurologic form of the virus is quite contagious and can easily be passed from horse to horse.

Horses affected with EHM show signs of illness that begin with fever and possibly some mild respiratory issues such as runny nose, sneezing, and cough.

Over the next several days, nervous system problems may develop. These signs may include incoordination, weakness or paralysis of one or more legs (which might look like lameness), muscle tremors, loss of tail and bladder function and, finally, an inability to rise.

Infected horses spread the EHV virus mostly through breathing and fluids from the nose and mouth.

Close contact with an infected horse is usually necessary for a horse to catch the virus, but buckets, halters and other tack can carry the virus from one horse to another.

An infected horse can be a source of infection even before they start showing serious signs of illness.

Horse owners can take steps to prevent EHM from affecting their horses:

– During events, limit the horse’s contact with other horses and equipment used by other horses.

– When arriving home, keep the horse separate from other horses for a period of three weeks. This will allow for easier recognition of illness and will prevent the spread to horses that have remained at home. Limit person and equipment contact between the isolated horse and other horses. Avoid bringing the horse to events until after that time period has passed.

– Clean and disinfect any equipment, tack or trailers that accompanied the horse to the event.

– Keep horses up to date on routine preventive vaccines and parasite control.

While current “rhino” vaccines do not appear to protect against neurologic strains of EHV, preventing these other illnesses will prove valuable in restoring the health of a horse potentially affected with EHM.

In addition, all horse owners should obtain the necessary Certificates of Veterinary Inspection/health papers when horses cross state lines.

Certain horse events may require these papers regardless of the horse’s origin. This practice not only ensures that horses showing early signs of illness do not travel and spread it to others, it also allows for officials to contact horse owners promptly if their horse has unknowingly been exposed to an EHV-infected horse.

When signs of EHM are suspected, a horse owner should promptly contact their veterinarian. Take care to isolate the affected horse from others as soon as possible, limit visitor traffic, and manage tack and equipment so other horses are not exposed. The veterinarian may take nasal swab samples for a diagnosis, but this is usually only successful early in the course of the disease.

There is no specific treatment or cure for EHM, so veterinarians will outline a course of supportive care. Despite these best efforts, in many horses, the disease progresses to the point where euthanasia is necessary.

For more information about EHM and your horse’s health, contact your local veterinarian. The South Dakota Animal Industry Board ( and SDSU Extension ( also have information about EHM.

–SDSU Extension

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