Toxoplasma-like Encephalomyelitis in the Horse

Eight horses with progressive neurologic signs had encephalomyelitis associated with toxoplasma-like protozoan bodies. There were scattered hemorrhagic, malacic lesions in white and grey matter in the brain and spinal cord. Microscopically there was malacia, mononuclear cell infiltration, especially perivascularly, gliosis, and various degrees of necrosis and hemorrhage. Other tissues were normal, except for the lung of one horse that had focal bronchopneumonia. The cerebrospinal fluid did not contain measurable amounts of IgM, IgG, or IgA. Serum from one horse was negative at 1:64 by the hemagglutination-inhibition test for toxoplasma antibodies.