Equine herpes myeloencephalopathy.

The neurologic form of EHV-1 infection appears to be the result of central nervous system infarction caused by vasculitis, which is initiated in endothelial cells of small blood vessels. The etiologic agent is equine herpesvirus-1, subtype 1. There is some evidence to suggest that the neurologic form of the disease actually results from reactivation of a previous infection. Whether the vasculitis that causes the central nervous system injury is the direct result of the infection or an immune response to the infection has not been determined. The clinical signs are rapid in onset, nonprogressive, and many horses may improve. The diagnosis must often remain tentative, particularly in horses that recover, because there is no single reliable confirmatory test. The prognosis is generally good, although recovery may be slow and incomplete. Supportive therapy is essential, and administration of corticosteroids may be useful. There is no specific therapy for the virus or for the vasculitis. Currently no vaccine can be claimed to protect against the central nervous system form of the disease. Vaccination is recommended, however, to reduce the incidence of respiratory disease, abortion, and neonatal death on the farm. Repeated vaccination is necessary to maintain presumably protective antibody concentrations. Vaccination every 3 to 4 months may decrease the incidence of EHV-1 infection on the farm and therefore may indirectly prevent the occurrence of the neurologic form of the disease.