Role of Toxoplasma Oocysts for Spread of Swine Toxoplasmosis

Swine toxoplasmosis is one of the most important diseases of pigs in Japan. Toxoplasma is a causal agent of zoonoses infecting not only swine, but also many kinds of mammals, including man. Therefore, routes of infection have been examined in toxoplasmosis of man and animals. Congenital transmission has already been confirmed in man and animals, but no acquired infection has been fully understood as yet. It is well known that animals are infected by eating fresh meat containing Toxoplasma cysts. However, the presence of any other route for toxoplasmosis has not been determined in s,vine as in some other animals until recently. More recently, the coccidial stage of Toxoplasma was clarified 1 >. When cysts of Toxoplasma were given orally to a cat, oocysts began to be discharged in the feces of the cat 4 or 5 days after cyst inoculation. The oocyst of Toxoplasma was identical with that of the small type of lsospora bige1nina2>. Toxoplasma oocysts, as well as other coccidial oocysts, showed a remarkable resistance to various kinds of disinfectants and other chemicals4>. Moreover, they survived more than 1 year under the usual climatic conditions in Japan. In the authors' unpublished data, they retained their infectivity to mice even after storage at 0-4°C for more than 3 years. Therefore, the oocysts seemed to be among the most important sources of Toxoplasma infection. Then, the authors inoculated Toxoplasma oocysts into piglets to examine the role of oocysts in the spread of toxoplasmosis.