Equine herpesvirus 1 myeloencephalopathy.

Myeloencephalopathy is an uncommon manifestation of equine herpesvirus 1 (EHV-1), but it can cause devastating losses during outbreaks on individual farms. Clinical signs of neurologic disease reflect a diffuse multifocal hemorrhagic myeloencephalopathy secondary to vasculitis and thrombosis. Sudden onset and early stabilization of signs, including ataxia, paresis, and urinary incontinence; involvement of multiple horses on the premises; and recent history of fever, abortion, or viral respiratory disease in the affected horse or herdmates are typical features, although there is considerable variation between outbreaks in epidemiologic and clinical findings. Prevention is difficult because many asymptomatic horses are infected latently with EHV-1 myeloencephalopathy and because vaccines do not confer protection against neurologic manifestations of infection. This article reviews the pathogenesis, pathology, clinical manifestations, diagnosis, and treatment of EHV-1 myeloencephalopathy and discusses prevention and control of equine herpesviral infections in the context of their epidemiology.