Hepatocystosis in a baboon (Papio anubis)

A 26-lb wild-caught adult female baboon was obtained from a commercial vendor. Routine tests for parasites, pathogenic bacteria, and tuberculosis were negative throughout the 10-week quarantine. However, routine radiographs performed at the end of the quarantine period detected multiple small radioopaque nodules evenly dispersed throughout the liver. A hepatic biopsy was obtained during routine ovariectomy of the baboon, and a diagnosis of granulomatous hepatitis made. Approximately 1 year after her arrival, the baboon was euthanized for reasons unrelated to the hepatitis. The liver contained multiple (40 to 50) white foci that were 1 to 3 mm in diameter; these foci were visible on the surface as well as throughout the parenchyma. There was multifocal, moderate capsular fibrosis, with adhesions between the hepatic lobes and between the diaphragm and liver. Histologic examination revealed multiple degenerate Hepatocystis sp. merocysts. H. kochi and H. simiae are malarial-type nonpathogenic protozoa endemic to Old World nonhuman primates, including baboons. Infected animals are asymptomatic and do not experience hemolysis. Transmission requires an insect vector, therefore infection with Hepatocystis sp. has minimal implications for colony health. There is no known danger of transmission to humans.