(Updated May 13, 2020)


EHM diagnosed in Ward County horse


BISMARCK – The North Dakota State Board of Animal Health and the North Dakota Department of Agriculture’s Animal Health Division are reminding horse owners to protect their horses from equine herpesvirus-1 (EHV-1). A horse in Ward County has been confirmed positive for equine herpesvirus myeloencephalopathy (EHM), the neurologic manifestation of the virus.  There were no recent movements of horses to or from the farm.  The horse is recovering under the owner’s care.

The last confirmed case of EHM in North Dakota was identified in December of 2019.

EHV-1 can be spread through the air, and on contaminated equipment, clothing and hands. Biosecurity measures that can reduce the risk of spreading the disease include avoiding shared food or water containers and preventing nose-to-nose contact.

Out-of-state horses and other equines entering North Dakota for any length of time must be accompanied by a Certificate of Veterinary Inspection. “Certificates of Veterinary Inspection help us better monitor the movement of equines into North Dakota and help determine potential sources of diseases,” said State Veterinarian Dr. Susan Keller.

EHV-1 can cause respiratory disease, abortion, neonatal death and sometimes the neurologic form of the disease, EHM. Vaccinations against EHV-1 have been shown to reduce viral shedding and curb the spread of disease, and may decrease the severity of infection. While no vaccine can completely prevent EHM, vaccinating healthy animals and giving booster vaccinations before travel, competition or boarding is recommended.

“Horse owners should discuss vaccination strategies and other preventative measures with their veterinarians,” Agriculture Commissioner Doug Goehring said.

Although highly infectious and contagious among horses, EHV-1 poses no threat to human health.




Equine herpesvirus-1 (EHV-1) is endemic to the United States. There are 4 manifestations of the disease: respiratory tract disease, abortion, neonatal mortality and a paralytic neurological disease. Horses that recover from the disease may become inapparent carriers and be biological reservoirs to transmit the disease to other horses.

Clinical signs may be nonspecific and a fever of a 102° F or higher may be the only thing seen. The incubation period is 2 to 8 days. Respiratory signs of a cough and nasal discharge may be seen along with the fever. Abortion is almost always seen in the last 4 months of gestation and there are no impending signs. The placenta is expelled with the fetus, which contains a high level of virus. Foals infected are born at term but are obviously sick at birth or become ill with in one or two days of birth. The foals fail to nurse, become lethargic and exhibit severe respiratory distress. Despite intensive supportive veterinary care foals die of viral pneumonia in a few days. Equine herpesvirus myeloencephalopathy (EHM), a neurological disease of horses caused by EHV-1, causes a horse to be weak, uncoordinated and have trouble standing. The rear limbs are more severely affected than the front creating the inability to rise from sitting position. There may be difficulty in urinating and defecating. Non-recumbent horses can have a favorable prognosis but those down longer than 24 hours have a poor prognosis.

The virus can spread through the air, contaminated equipment, clothing and hands. The virus does not last long in the environment and can be easily killed by disinfectant but a cough or sneeze can cause transmission up to 35 feet. Disinfection of premises, stalls and trailers is indicated. Not washing hands after handling a horse with EHV-1 can spread the disease. A solution of 1 part chlorine to 10 parts water is effective for decontaminating equipment and environment after removing gross dirt, debris and manure.

Once EHV-1 confirmation is made, quarantine or isolation measures to restrict the movement of all potentially exposed horses will be necessary to prevent the spread of the disease to other locations. Horses in the immediate contact area of the clinically affected horse should be tested as well as any showing clinical signs.  Isolation of sick horses is important along with early determination of the cause. Isolation of horses with a fever is a good practice in any case. If a horse develops fever, respiratory signs, or neurological signs, a veterinarian should be notified immediately. The horse and horses in the immediate area should not be moved except for the movement of the affected horse to an isolation stall or enclosure located away from high traffic areas.  Vaccination is not recommended on facilities experiencing active cases.

EHV vaccination should be part of a normal vaccination protocol for healthy horses. Horse owners should consult their veterianraian for specific recommendations. There are several commercially manufactured vaccines for controlling abortion and respiratory disease caused by EHV-1. No current vaccine will protect against the neurological manifestation or EHM. Annual boosters are required. Vaccination, along with good management practices, will decrease the severity of EHV-1 respiratory disease of young horses and limit the occurrence and severity of abortion storms.



Equine herpesvirus-1 Contacts

North Dakota State Board of Animal Health

600 East Boulevard Ave. Dept. 602 Bismarck, ND 58505-0020
doa-bah@nd.gov https://www.nd.gov/ndda/ndsbah