Analysis of risk factors for the development of equine protozoal myeloencephalitis in horses.

OBJECTIVE: To investigate risk factors for development of equine protozoal myeloencephalitis (EPM) in horses.
DESIGN: Case-control study. ANIMALS: 251 horses admitted to The Ohio State University Veterinary Teaching Hospital from 1992 to 1995. PROCEDURE: On the basis of clinical signs of neurologic disease and detection of antibody to Sarcocystis neurona or S neurona DNA in cerebrospinal fluid, a diagnosis of EPM was made for 251 horses. Two contemporaneous series of control horses were selected from horses admitted to the hospital. One control series (n = 225) consisted of horses with diseases of the neurologic system other than EPM (neurologic control horses), and the other consisted of 251 horses admitted for reasons other than nervous system diseases (nonneurologic control horses). Data were obtained from hospital records and telephone conversations. Risk factors associated with disease status were analyzed, using multivariable logistic regression.
RESULTS: Horses ranged from 1 day to 30 years old (mean +/- SD, 5.7 +/- 5.2 years). Risk factors associated with an increased risk of developing EPM included age, season of admission, prior diagnosis of EPM on the premises, opossums on premises, health events prior to admission, and racing or showing as a primary use. Factors associated with a reduced risk of developing EPM included protection of feed from wildlife and proximity of a creek or river to the premises where the horse resided. CONCLUSIONS AND CLINICAL RELEVANCE: Development of EPM was associated with a number of management-related factors that can be altered to decrease the risk for the disease.