) of those exposed will become ill with symptoms. Native wild birds infected are not likely to show any symptoms, however non-native birds become acutely ill and die from S. falcatula exposure. (U. Missouri… 1999)Primary clinical signs of EPM occur from swelling and nerve death in the central nervous system as a result of the replicating protozoa. Neurologic signs can be directly referable to the site or sites of infection. The spinal cord is most often affected resulting in the “three A” symptoms of asymmetric ataxia and focal muscle atrophy. (Fenger, 1996) Ataxia affects the horse’s sense of position in space. When the nerves in the inner ear are damaged the horse loses unconscious proprioception which is the directional sense of up and down. When the conscious proprioception tracts from the joints and muscles of the legs are damaged the animal loses its sense of limb position in space. (Fenger, 1995) Ataxia is associated with the staggering “drunken sailor” gait used to describe animals with neurological dysfunction, and can be rated on a scale of one to five. Five being a horse which cannot stand up and one being a horse which is unlikely to fall and looks normal walking strait but can be made to show deficit when turning, or going up and down an incline. Horses with EPM can exhibit any level of ataxia from mild to severe however often horses’ symptoms will be asymmetric (more severe on one side) and be combined with focal muscle atrophy (wasting and weakness) especially in the hindquarters. (Fenger, 1995) It is important to note that often the only signs of EPM may be a slight gait asymmetry or apparent lameness that fails to block out in a comprehensive lameness exam. Therefore the disease may not be apparent to the lay person in its early stages. (Fenger, 1996) EPM is often overlooked in the ten percent of horses that experience airway problems as a result of cranial nerve dysfunction. Be...
