Context: Enterocytozoon bieneusi is the most frequent microsporidian parasite of human patients with acquired immunodeficiency syndrome and is a significant cause of diarrhea and wasting. Recently, this organism has also been recognized as a spontaneous infection of several species of captive macaques. As in humans, E bieneusi frequently causes enteropathy and cholangiohepatitis in immunodeficient simian immunodeficiency virus (SIV)-infected macaques.
Objective: To examine E bieneusi as an etiologic agent of nonsuppurative proliferative serositis in immunodeficient rhesus macaques (Macaca mulatta).
Design: Retrospective analysis of necropsy material obtained from immunodeficient SIV-infected rhesus macaques.
Results: Examination of SIV-infected rhesus macaques (n = 225) revealed E bieneusi proliferative serositis in 7 of 16 cases of peritonitis of unknown origin. The organism could be identified by in situ hybridization and polymerase chain reaction in sections of pleura and peritoneum obtained at necropsy. Serositis was always accompanied by moderate-to-severe infection of the alimentary tract, and morphologic evidence suggested dissemination through efferent lymphatics. Colabeling experiments revealed most infected cells to be cytokeratin positive and less frequently positive for the macrophage marker CD68. Sequencing of a 607-base pair segment of the small subunit ribosomal gene revealed 100% identity to sequences obtained from rhesus macaques (Genbank accession AF023245) and human patients (Genbank accession AF024657 and L16868).
Conclusions: These findings indicate that E bieneusi disseminates in immunodeficient macaques and may be a cause of peritonitis in the immunocompromised host.