EQUINE HERPESVIRUS (EHV) IN PREGNANT MARES

Equine herpesvirus type 1 and equine herpesvirus type 4 (EHV-1 and EHV-4) are viruses that can cause a variety of serious illnesses in the horse ranging from inapparent to severe infections, including respiratory distress, fever, nasal discharge, cough, inappetence, neurological disease (loss of coordination or ability to stand), and abortions in pregnant mares.

EHV is common in many equine populations because when the horse is infected with the virus, the virus can become latent (dormant) and may re-appear during times of stress or illness, which can lead to infections of other horses. EHV is spread through the air, through contact with respiratory or nasal secretions, and by exposure to infected fetal tissues/fluids.

EHV-1 can cause abortions and stillbirths in pregnant mares exposed to the virus. It is important to properly dispose of the placenta and thoroughly disinfect the foaling area, especially if the mare foaled unexpectedly and prematurely (320 days gestation or less). Neonatal foals infected with EHV-1 at or near the time of foaling may suffer severe illness that is fatal. In addition,EHV-1 can also affect the central nervous system (brain and spinal cord), resulting in clinical signs such as incoordination, paralysis, coma, and death. Treatment is primarily supportive care for any form of this disease.

Conscientious management and biosecurity measures will help prevent transmission of EHV to healthy horses. New horses introduced to the farm should be quarantined based on your veterinarian's recommendation and stabled separately from pregnant mares. The virus can be transmitted on people's hands, clothing, and shared equipment so restricting the movement of farm personnel and equipment is vital to helping contain the disease. It is important to be aware that horses, even after they are fully recovered, can remain carriers of the disease and may continue to shed the virus for a period of time. Infected horses should be isolated away from healthy horses and monitored for recovery over a 3-4 week period.

Maintaining adequate protection during pregnancy also requires vaccination with an inactivated EHV-1 vaccine licensed to help prevent abortions, during the fifth, seventh and ninth months of gestation. In areas where Equine herpesvirus abortions are especially prevalent, additional vaccinations may be recommended by your veterinarian.

Following precautions such as instituting a quarantine period for new horses to your property before introducing them to your barn, stabling pregnant mares separately from other horses and thoroughly disinfecting foaling areas will help to decrease transmission of Equine herpesvirus to horses on your farm.