E200
Equine Herpesvirus 1 and 4
(Rhinopneumonitis)

Causative Agent: This disease is caused by two different groups of viruses, EHV-4 and EHV-1. Equine herpes 4 (EHV-4) usually causes respiratory problems, while Equine herpes 1 (EHV-1) causes abortions.

Clinical Signs: An infected animal starts with a fever, nasal and eye discharge, coughing, and stops eating. Pregnant mares that are infected usually do not show significant symptoms until they abort 2-12 weeks after the onset of the initial infection. These abortions usually occur between the 7th and 11th month of gestation. Occasionally, animals infected with EHV-1 show neurologic signs like a lack of coordination, inability to move, and loss of tail and bladder function.

Disease Transmission: These viruses can be transmitted from one animal to another by direct contact, nasal secretions, contaminated buckets, feeders, halters, and other equipment.

Diagnosis: Based on clinical signs, it is difficult to tell the difference between a herpes respiratory infection and equine influenza or viral arteritis. However, it is possible to isolate the herpes virus by using nasal swabs and transtracheal washes. When looking for titers specific to herpes, blood from the infected animals can also be used. Use of the aborted fetus is also very beneficial in diagnosing this disease. Blood samples from mares that abort are usually not that helpful; by the time the mare aborts, the titers in the blood are too low to be diagnostic.

Treatment: It is important to understand that treatment of viral infections involves treating the symptoms and not killing the organism. Treatment for the respiratory problems of this disease include the following:

  1. Strict rest (3 weeks).
  2. Keeping the animal out of dry, dusty, or stressful environments.
  3. Non-steroidal anti-inflammatory drugs (bute or Banamine).
  4. A broncho-dilater (Ventipulmin).
  5. Possible antibiotics for secondary bacterial infections.

Prevention: Vaccination programs are the best prevention. See the vaccination schedule recommendations on page A905. Isolation of animals for 3-4 weeks after they enter a new location is always a good idea. It is particularly important in situations where a new animal may be in contact with any pregnant animals.