Equine Neurological Dysfunction

just a few of the different ways in which illness or injury can affect the equine nervous system.
To get to the bottom of his mysterious lameness problem Beaus owner called out her veterinarian to examine him. A physical examination revealed that Beau seemed in overall good health. He was bright and alert in an ideal body condition and his heart lungs and gastrointestinal tract were all in good working order. However the veterinarian noticed a subtle abnormality that provided a clue towards the diagnosis Beau had noticeable loss of muscle or atrophy in his left hindquarter region. 
To assess his gait the veterinarian put Beau through his paces in a full soundness evaluation. The gelding did have an asymmetric gait in his hind limbs and closer assessment revealed an intermittent lameness in his left hind. As the observers had previously noted he would occasionally drag his toe or take a wide step with the left hind. Overall the leg just seemed weak. However no pain heat or swelling was detectable on examination and no amount of flexion or manipulation of the limb could elicit a pain response in Beau. Based on these findings a neurological examination was performed and showed that Beau had difficulty placing his left hind correctly when turning in a tight circle or backing up. Unfortunately the cause of the geldings gait abnormality was now clear he had neurological dysfunction resulting in ataxia or incoordination in his left hind.
WHAT SHOULD BE DONE NEXT? There are various diseases of the CNS or PNS that may cause ataxia in the horse. In Beaus case the asymmetrical distribution of the ataxia and muscle atrophy hinted at a likely cause Equine Protozoal Myeloencephalitis or EPM which is a neurological disease caused by a protozoan singlecelled parasite called Sarcocystis neurona. Another parasite Neospora hughesi causes identical clinical signs but is far less common than S. neurona. The parasite is shed in the feces of the opossum Didelphis virginiana which has a widespread geographic range throughout North and Central America. In Canada its range is restricted to southern Ontario and British Columbia. Horses become infected when they are exposed to the feces of an infected opossum usually through contaminated feed or water. The protozoan parasite then multiplies within the horses body and localizes in the CNS. The spinal cord is the most commonly affected part of the nervous system but brain lesions also
 occur. Asymmetrical clinical signs are a classic finding in EPM cases but in some cases symmetrical neurological deficits are found.
Beaus veterinarian had a hunch that he was affected by EPM and therefore needed samples to send to the laboratory to achieve a diagnosis. Blood and cerebrospinal fluid were collected and sent off for analysis. The results confirmed the veterinarians clinical suspicion Beau had high antibody titres for S. neurona in both his blood and cerebrospinal fluid.