Maryland Department of Agriculture

Today's Update

Article on recommendations for equine herpesvirus-1 prevention and control by George P. Allen, Department of Veterinary Science, M. H. Gluck Equine Research Center, University of Kentucky, Lexington, Kentucky 40546-0099, USA

The following description is from the Merck Veterinary Manual Ninth Edition, pp. 1203-1205.
Equine herpesvirus 1 (EHV-1) and EHV-4 comprise two genetically and antigenically distinct groups of viruses that have been referred to as subtypes 1 and 2 of EHV-1. Both viruses are ubiquitous in horse populations worldwide. Each produces an acute febrile respiratory disease (Rhinopneumonitis).

An infrequent clinical sequela of EHV-1 infection, which is caused solely by certain strains of EHV-1, is development of neurologic disease. The natural reservoir of both EHV-1 and EHV-4 is the horse. Transmission occurs by direct or indirect contact with infective nasal discharges, aborted fetuses, placentas, or placental fluids.

Equine viral rhinopneumonitis cannot be clinically differentiated from equine influenza, equine viral arteritis, or certain other equine respiratory infections solely on the basis of clinical signs

Immunity after natural infection with EHV-1 or EHV-4 appears to involve a combination of both humoral and cellular immune factors. Most horses are latently infected with EHV-1 and EHV-4. Immunity to reinfection of the respiratory tract may persist for up to 3 months.

For prevention and control of EHV-4 and EHV-1 related diseases, the following management practices are recommended. Introduction of the virus into a susceptible group of horses from an exogenous source should be avoided. Horses arriving on a farm from other farms or sales or returning from the racetrack should be isolated for 3-4 weeks before commingling with resident horses, especially with pregnant mares. This is especially relevant with respect to pregnant mares, which if possible should be maintained in a group away from weanlings, yearlings, and horses out-of-training. In an outbreak of respiratory disease or abortion, affected horses should be isolated, and appropriate sanitary measures taken.

More information about equine herpesvirus and biosecurity practices can be found through the following links: