Four clinical syndromes have been attributed to equine herpes virus-1 (EHV-1): respiratory disease in younger horses, abortion in pregnant mares, stillbirth or weakness in newborn foals and paralysis ( equine herpes virus myeloencephalopathy (EHM)).
EHM has been identified more frequently in recent years. Knowledge gained through dealing with outbreaks of the disease is now available in a 74 page report published by the USDA Animal and Plant Health Inspection Services, Centers for Epidemiology and Animal Health.
The report, Equine Herpesvirus Myeloencephalopathy: Mitigation Experiences, Lessons Learned, and Future Needs is based on interviews with 18 veterinarians or state equine program managers who worked to control recent outbreaks of the disease. You can download a copy here.
Dr. Josie Traub-Dargatz, Equine Commodity Specialist at Colorado State University and Dr. Barbara Bischoff,Veterinary Analyst, USDA:APHIS:VS:CEAH, Fort Collins, Colorado discuss the report in the July edition of the Equine Disease Quarterly published by the Maxwell H Gluck Equine Research Center, University of Kentucky. They write:
“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.”
Also available is an educational brochure about EHM produced by USDA Animal and Plant Health Inspection Service: Veterinary Services. Entitled Equine Herpesvirus (EHV) Myeloencephalopathy: A Guide to Understanding the Neurologic Form of EHV Infection, it is available here .