Experimental Infection of Horses with Culture-Derived Sarcocystis neurona Merozoites as a Model for Equine Protozoal Myeloencephalitis

A study was designed to develop an experimental model to produce Sarcocystis neurona encephalitis in horses. Sarcocystis neurona, isolated from the spinal cord of an ataxic horse, was placed in continuous culture using bovine turbinate cells, and the cultured S. neurona merozoites were used to infect lymphocytes. A horse that was subsequently experimentally infected with 100,000 of the S. neurona-infected lymphocytes developed encephalitis and ataxia. Sarcocystis neurona was isolated from the spinal tissues of the infected horse by in vitro culture. Three horses, each infected with a different number of merozoiteinfected lymphocytes, were used to estimate an infective dose of parasites needed to induce clinical signs of equine protozoal myeloencephalitis. This is the first report of histologically confirmed experimental