Antibody to neuritogenic myelin protein P2 in equine paresis due to equine herpesvirus 1

Miscellaneous neurologic or neuromuscular disorders in horses

NMD is an important cause of morbidity in horses. Signs of dysfunction could be variable depending on the specific area affected. NM disease can go unrecognized if a thorough evaluation is not performed in diseased horses. Electrodiagnostic testing is an area that has the potential to document and improve our understanding of NM disease yet is uncommonly performed. Keeping an open and observant mind will enhance our ability to search and find answers.

Equine herpesvirus-1 myeloencephalopathy: a review of recent developments

Equine herpes myeloencephalopathy (EHM), although a relatively uncommon manifestation of equine herpesvirus-1 (EHV-1) infection, can cause devastating losses on individual farms or boarding stables. Although outbreaks of EHM have been recognized for centuries in domestic horse populations, many aspects of this disease remained poorly characterized. In recent years, an improved understanding of EHM has emerged from experimental studies and from data collected during field outbreaks at riding schools, racetracks and veterinary hospitals throughout North America and Europe. These outbreaks have highlighted the contagious nature of EHV-1 and have prompted a re-evaluation of diagnostic procedures, treatment modalities, preventative measures and biosecurity protocols for the disease. This review concentrates on these and other selected, clinically relevant aspects of EHM.

Cerebrospinal Fluid

This chapter discusses the anatomy, functions, and biochemistry of cerebrospinal fluid (CSF). CSF has four major functions: physical support of neural structures, excretion and “sink” action, intracerebral transport, and control of the chemical environment of the central nervous system. CSF provides a “water jacket” of physical support and buoyancy. The CSF is protective because its volume changes reciprocally with changes in the volume of intracranial contents, particularly blood. Thus, the CSF protects the brain from changes in arterial and central venous pressure associated with posture, respiration, and exertion. Acute or chronic pathological changes in intracranial contents can be accommodated, to a point, by changes in the CSF volume. The direct transfer of brain metabolites into the CSF provides excretory function. This capacity is important because the brain lacks a lymphatic system. The lymphatic function of the CSF is also manifested in the removal of large proteins and cells, such as bacteria or blood cells, by bulk CSF absorption. The “sink” action of the CSF arises from the restricted access of water-soluble substances to the CSF and the low concentration of these solutes in the CSF.

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.

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.