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Published April 14, 2014, 09:14 AM

Equine Herpesvirus identified in US

BROOKINGS, S.D. — Cases of Equine Herpesvirus (EHV) have been identified across the U.S. It is imperative that horse owners recognize the clinical signs of EHV, and understand how it is transmitted and how to prevent it.

By: SDSU Extension Service ,

BROOKINGS, S.D. — Cases of Equine Herpesvirus (EHV) have been identified across the U.S. It is imperative that horse owners recognize the clinical signs of EHV, and understand how it is transmitted and how to prevent it.

EHV is a virus that rears its head in horse populations around the nation. There are two strains of the virus (EHV-1 and EHV-4) that account for the majority of EHV infections. EHV is easily spread among horses through close contact. The disease generally manifests through three syndromes (signs) including respiratory infection (“rhinopneumonitis”), abortion and neurological disease.

Clinical signs

Rhinopneumonitis: Signs might be mild or unapparent in horses that have been vaccinated. The respiratory infection is often seen in younger horses such as weanlings and causes symptoms such as fever, nasal discharge, cough and swelling of lymph nodes. This syndrome is caused by EHV-4 and is commonly followed by a secondary bacterial infection.

Abortion: Infection with EHV-1 is associated with late-term abortion (seven to 11 months of gestation). In rare occasions, exposed mares can give birth to a live foal. But, the foals are often weak with this viral infection and secondary bacterial infections and usually only live a few days.

Neurological disease: This syndrome is caused by EHV-1. Symptoms include incoordination, lameness, loss of tail and bladder function and paralysis, depending on which part of the nervous system is affected.

Diagnosis, treatment and prevention

Diagnosis of EHV can be difficult and time sensitive. If you suspect EHV, it is important to enlist the help of your veterinarian. Generally nasal swabs or blood samples can be collected to test for EHV.

In most cases, treatment of EHV is supportive, meaning symptoms as they arise. Unfortunately the disease can progress to the point where euthanasia is the only option.

Vaccinations for both EHV-1 and EHV-4 are available. But, they do not prevent the neurological signs associated with EHV. Initial vaccination of foals begins at three to four months of age with a booster four to eight weeks later. Subsequent boosters are recommended every three to six months to maintain an adequate level of protection in the horse. Veterinarians should be able to help determine which EHV vaccinations to select and how often to vaccinate based on the specific risk factors for each horse. Horses that are frequently traveling and coming into contact with other horses should likely receive boosters every 90 days. Pregnant mares should be vaccinated with an EHV vaccine that is labeled for prevention of equine abortion at three, five, seven and nine months of gestation.

Additional management practices can help limit the risk of EHV on your property. When you have a new horse arrive on your property adhere to a strict three- to four-week isolation period. If during this time no signs of illness arise in the new horse, they may be introduced to the herd. Try to only attend events where health certification and vaccination requirements are enforced. Finally, cleanliness and disinfection of trailers, water buckets and other equipment will help prevent the spread of EHV and other communicable diseases.

For more information on EHV contact Rebecca Bott, South Dakota State University Extension equine specialist at Rebecca.Bott@sdstate.edu, or Russ Daly, SDSU Extension veterinarian at Russell.Daly@sdstate.edu. To report a case of EHV in South Dakota, contact Dustin Oedekoven, State Veterinarian.

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