Equine Protozoal Myeloencephalitis

Abstract

Gathering information about Equine Protozoal Myeloencephalitis (EPM) was identified by the equine industry as one of the highest priorities for the NAHMS Equine '98 study. Overall, 59.8 percent of owners/operators interviewed had never heard of EPM, and only 9.5 percent considered themselves knowledgeable about this disease. EPM was reported to have occurred on 1.0 percent of operations in the year prior to the study and on 3.3 percent of operations at any point in the operation's history. The incidence of EPM was estimated in the year prior to the study to be 14 new cases per 10,000 horses per year. The majority of operations where EPM was reported had only identified a single case at any time during their history. While this study was based on owner/operator reports of disease, 95.0 percent of cases recognized during the year prior to this study were diagnosed by a veterinarian. Onset of disease was reported most commonly to occur during the summer or fall. The most common signs reported in cases occurring during the previous year were ataxia, limb weakness, lameness, and muscle atrophy. The most common methods used to diagnose EPM in these horses were recognition of clinical signs, serology, and CSF analysis. Among the last cases recognized on operations for which duration of illness was at least 3 months, 39.7 percent were reported to recover completely, 37.4 percent improved but did not completely recover, 14.4 percent were sold or given away because they had EPM, and 7.1 percent died or were euthanatized because of EPM. For those EPM cases that completely recovered, relapsed following improvement and showed no improvement after at least 3 months' duration, the average number of days of lost use was 244 days. For those EPM cases that died because of EPM, an estimated 9.2 years of use were lost. Excluding cases that were less than 3 months in duration, the geometric mean cost to operations for diagnostic testing, veterinary care, and medications provided for the last diagnosed case of EPM was $790. EPM was reported to occur rarely in this study population, despite the use of owner reports to measure disease occurrence. Veterinarians were almost always employed in the diagnosis of this disease for cases occurring in the previous year. Despite its rare occurrence, this disease is a very serious health problem in affected horses and only about 40 percent of affected horses were reported to have recovered completely. Equine protozoal myeloencephalitis (EPM) is a serious and often fatal neurologic disease of equids. 1-6 Ammals affected by EPM can demonstrate a variety of clinical abnormalities, and signs can vary tremendously in severity. Classically, horses with EPM develop a variety of asymmetric neurologic deficits including gait abnormalities, ataxia, weakness, and focal muscle wasting. 4-6 However, symmetric neurologic abnormalities are also seen frequently. The disease may be focal or multifocal in nature and may be manifested less frequently as a head tilt, facial paralysis, seizures, or even apparent behavioral changes. 4-6 Horses of all ages can be affected, but horses are usually at least 6 months old when first diagnosed with EPM.