IDENTIFICATION OF AN ENTEROCYTOZOON BIENEUSI-LIKE MICROSPORIDIAN PARASITE IN SIMIAN-IMMUNODEFICIENCY-VIRUS-INOCULATED MACAQUES WITH HEPATOBILIARY DISEASE

Enterocytozoon bieneusi is a common opportunistic pathogen of human pa tients with acquired immune deficiency syndrome (AIDS) causing signifi cant morbidity and mortality, In a retrospective analysis utilizing co nventional histochemical techniques, in situ hybridization, polymerase chain reaction, and ultrastructural examination, we identified 18 sim ian-immunodeficiency-virus-infected macaques (16 Macaca mulatta, 1 M. nemestrina, and 1 M. cyclopis) with Enterocytozoon infection of the he patobiliary system and small intestine, The organisms were readily ide ntified in the bile ducts and gall bladder by special stains and by in situ hybridization using a probe directed against the small subunit r ibosomal RNA of human origin E. bieneusi. Infection of the biliary sys tem was associated with a nonsuppurative and proliferative cholecystit is and choledochitis, Hepatic involvement was characterized by bridgin g portal fibrosis and nodular hepatocellular regeneration accompanied by marked bile ductular and septal duct hyperplasia. Ultrastructurally , all developmental stages of the organism were found in direct contac t with the host cell cytoplasm; spores and sporoblasts contained a dou ble layer of polar tubes. Sequencing of a 607-bp segment of the small subunit ribosomal RNA revealed 37 and 100% identity to two clones of s mall subunit ribosomal RNA derived from E. bieneusi of human origin, E xtensive morphological and genetic similarities between the simian and human enterocytozoons suggest that experimentally infected macaques m ay serve as a useful model of microsporidial infection in AIDS.