b'worse prognosis than those with WNV. Fifty to 90% of infected horses showing clinical signs of EEE do not survive, with many victims dying within two to three days of disease onset. After the virus invades the central nervous system, encephalitis (inflamma-tion of the brain) occurs, characterized by signs such as: Fever; Severe depression and behavior changes; Impaired vision; Circling or head-pressing; Muscle-twitching, paralysis of the STEPHANIE L. CHURCH/THE HORSEcranial nerves that control the facial muscles (frequently apparent as an in-ability to swallow); and Convulsions, paralysis, recumbency, and death.Long-term consequences Veterinarians have noted a high incidence of residual neurologic deficits among horses that doA veterinarian checks for neurologic signs during a prepurchase exam.recover from EEEmore than what is seen in horses that have had West Nilea head tilt, depression, facial nerve paral- Current treatment recommendations virus. In fact, Long says most horsesysis, difficulty swallowing, upper airwayinclude: surviving EEE infection exhibit long-termdysfunction, dorsal displacement of the Marquis and Protazil, which both neurologic signs, such as those listedsoft palate, and even laryngeal hemiple- contain the benzene acetonitrile agents above. When these are severe enough, thegia (paralysis of the nerve that controlsdiclazuril or toltrazuril. Studies show horses are often deemed unfit for riding. one of the arytenoid cartilages in thethat 62-67% of horses receiving these airway, which causes roaring). When thedrugs might improve one neurologic Equine Protozoal Myeloencephalitis brainstem and spinal cord are involved,grade or test negative for antibodies Horses pick up the protozoan parasitesdamage to their gray matter (whichagainst S. neurona in cerebrospinal (Sarcocystis neurona or, less commonly,processes impulses that, in turn, controlfluid (CSF). An estimated 10% of Neospora hughesi) responsible for thismuscle movement) and resulting gaithorses relapse following the standard neurologic disease after ingesting con- abnormalities that can easily be confused28-day treatment (Pusterla, 2017). taminated food or water; the parasiteswith lameness might result in asymmetric ReBalance, a sulfadiazine/pyrimeth-definitive host, the opossum, sheds themmuscle atrophy. Often, this degenerationamine oral suspension that inhibits in its feces. The parasites then migrateoccurs in the quadriceps muscles, whichDNA formation in the parasites. Treat-to the brain and spinal cord and causeare responsible for extending the stiflement is long-term (approximately 90 inflammation there. While all horses arejoint; gluteal muscles, which control hipdays or more) and might result in an at risk of infection, not all infected horsesmotion and limb rotation in the hind end;improvement of at least two neurologic develop disease. How many parasites areand the temporal muscles that help closefunction grades in 60-70% of treated at play and whether the horses immunethe jaw. horses. Approximately 10% of horses system is functional or suppressed areLong-term consequences The morerelapse following treatment (Pusterla, key to determining which horses suc- damage the parasites cause in a horses2017).cumb to infection.central nervous system, the higher hisPusterla and other EPM researchers Due to the causative agents unpredict- chances of either a poor outcome or fail- say these products efficacy is compa-able travel itinerary through the horsesure to recover fully following treatment.rable, treatment should continue until no CNS and our inability to guesstimateThere is a direct link between severityfurther clinical improvement occurs, and where they might damage the brain and/ of pathological changes and outcome,relapse can occur.or spinal cord, there are no classicincluding the presence of residualResearch in this field is focusing clinical signs of disease. Instead, signsclinical signs despite treatment, sayson the impact of extending treatment and their severity vary considerablyNicola Pusterla, DVM, PhD, Dipl. ACVIM,times, combining the use of these FDA-depending on what regions of the centralprofessor of equine internal medicineapproved products, using higher doses, nervous system the parasites damage.in the University of California, Davis,prophylactic (preventive) and prolonged/For example, if they damage the brainDepartment of Veterinary Medicine andmaintenance therapy, and the concurrent and cranial nerves, the horse can developEpidemiology. use of immunomodulators, he says.TheHorse.com | The HorseSeptember 201919'