Equine Herpesvirus Myeloencephalopathy Resources Available

A 74-page report on equine herpesvirus myeloencephalopathy (EHM), for which equine herpesvirus-1 (EHV-1) has been identified as a causative agent, was released by the USDA Animal and Plant Health Inspection Services, Centers for Epidemiology and Animal Health in July 2008.

The report, "Equine Herpesvirus Myeloencephalopathy: Mitigation Experiences, Lessons Learned, and Future Needs" (see PDF) is based on interviews with 18 veterinarians or state equine program managers who worked to control recent outbreaks of EHM.

In all situations discussed in the report, control strategies were implemented once an EHM case was identified because further spread of the virus was possible. Horse movement was stopped. In some instances the state veterinarian imposed an official quarantine, and in others, horse movement was voluntarily halted by the veterinary hospital or racetrack or stable owner. The body temperatures of potentially exposed horses were monitored in all outbreaks in order to quickly detect any fever and thus a potential EHV infection.

Potentially exposed but clinically normal horses were tested in some outbreaks but not in others. Some of the veterinarians and equine program managers interviewed for the report indicated that this testing allowed them to determine the potential for future cases of EHM. Others indicated that, given the difficulty of test interpretation for these horses and limited knowledge about the risk they pose, there was no reason to test. Commonly used biosecurity methods included restricting traffic of people into the area where affected horses were housed; using barrier precautions; and prohibiting the sharing of all equipment, including tack, water buckets, and tongue ties. In several of the outbreaks the affected horses were moved off-site to an isolated area, thereby reducing the viral challenge for horses initially housed in the same barn as the affected horse. Continual monitoring of exposed horses and off-site isolation of affected horses expedited a return to normal activities. At racetrack venues, protocols were developed that allowed potentially exposed horses to exercise without increasing the risk to unexposed horses.

A number of those interviewed for the report emphasized the need for clear, concise, and accurate communication regarding the plan for outbreak control. A person with infection control experience needs to be on site to review the protocols with caretakers of affected and exposed horses in order to be certain that all methods of disease transmission are adequately managed.

An educational brochure about EHM has been developed by USDA Animal and Plant Health Inspection Service: Veterinary Services. This resources is entitled "Equine Herpesvirus (EHV) Myeloencephalopathy: A Guide to Understanding the Neurologic Form of EHV Infection" (see PDF).  

To obtain hard copies of the report and brochure, call Abby Fienhold 970/494-7252 or e-mail: NAHMS@aphis.usda.gov.  

Contact: Dr. Josie Traub-Dargatz, 970/221- 4535; Colorado State University, Equine Commodity Specialist; USDA:APHIS:VS CEAH, Fort Collins, Colo.
Dr. Barbara Bischoff, 970/494-7001; Veterinary Analyst USDA:APHIS:VS CEAH, Fort Collins, Colo.

This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.