Neospora caninum causes abortion of cattle and the disease is one of the notifiable diseases in Japan. An immunohistochemical detection of Neospora parasites is the most reliable method which can be used for definite diagnosis of the disease. To improve reliability of the imunohistochemical diagnosis of bovine neosporosis, we examined distribution of the parasites in tissues of 18 aborted fetus which had characteristic histological lesions for neosporosis, including nonsuppurative encephalitis, carditis and myositis. Neospora tachyzoites and/or cysts were most frequently detected in the brain (83.3%), followed by the kidney (33.3%), tongue (25.0%) and spinal cord (21.8%). In addition, hyperimmune rabbit serum was produced using Neospora tachyzoites isolated in Japan. The serum was succesefully used for the immunohistochemical detection of Neospora, but not for Toxoplasma. Two monoclonal antibodies were raised against Neospora tachyzoites. Immunohistochemically, the antibodies reacted with Neospora, but not with either Toxoplasma nor Sarcosytstis. Immuno-gold electronmycroscory revealed that the antibodies reacted with dense bodies of Neospora tachyzoites. As shown above, it was suggested that the most reliable tissues for the detection of Neospora in aborted fetus were brain, spinal cord, and kidney. Antibodies have been supplied to prefectural veterinary diagnostic laboratories. (Infectious Disease Pathology Section, Department of Infectious Diseases TEL +81-29-838-7837)
