Abstract
Histopathological examination was carried out on the hepatic lesions of hepatocystosis in eighteen cynomolgus monkeys (Macaca fascicularis) from Southeast Asia, and the pathogenesis was discussed. The lesions caused by the protozoa were found only in the liver, showing the stages of exoerythrocytic schizogony of Hepatocystis, i.e., formation of merocysts and release of merozoites, with degenerative and/or progressive changes of the hepatic tissue. In these lesions, immature or mature merocysts unreleasing merozoite were destroyed and replaced by the granulation tissue. Early stage of the development of schizont and the necrotic lesions caused of release of merozoites from mature merocysts with the host reaction were found in a few monkeys within 20 days after imported into Japan. The disease without rupture of merocysts was not so harmful to the host animal, and the monkeys who passed a sufficient quarantine period could be utilized for experimental purposes. The parasite of the present cases was identified to be Hepatocystis semnopitheci by its characteristic structure of merocyst and the geographical localization of the host animals.
