S. neurona is a one-celled protozoan, similar to the parasite that causes malaria. The parasite is picked up orally by the horse from infected food or water. Only a small percentage of the horses which pick up the parasite become sick. Where the organism invades the CNS determines what clinical signs the horse exhibits. Clinical signs can include anything from dragging a toe, incoordination, or drooped lip or eyelid to complete recumbency and death.
Current treatment utilizes pyrimethamine and sulfadiazine.
Current treatments do not kill the parasite in the horse. Horses on current treatment also should get folic acid supplementation. Early detection and treatment usually aid in successfully combating the disease. A positive blood serum test only means the horse has been exposed to the parasite, not that it has or will develop disease. Antibodies found in cerebral spinal fluid, along with neurologic signs, are positive indicators of disease.