ULTRASTRUCTURE OF ATYPICAL (TERATOID) SPOROGONIAL STAGES OF ENTEROCYTOZOON-BIENEUSI (MICROSPORIDIA) IN NATURALLY INFECTED RHESUS-MONKEYS (MACACCA-MULATTA)

Objective.-To demonstrate the ultrastructural features of normal and a typical (teratoid) developmental stages of Enterocytozoon bieneusi in naturally infected rhesus monkeys (Macacca mulatta). Design and Method s.-Two rhesus monkeys with chronic simian immunodeficiency virus infec tion developed naturally acquired microsporidian infections. The gallb ladder had a high parasite burden and was evaluated by transmission el ectron microscopy. The microsporidian agent was confirmed as E bieneus i by polymerase chain reaction. Results.-In addition to normal sporogo nial plasmodia and spores of E bieneusi, abnormal teratoid structures were noted. These structures were greatly enlarged (up to 10 mu m) and were surrounded by an electron-dense exospore and electron-lucent end ospore typical of mature spores. Unlike mature spores, the abnormal st ructures contained multiple nuclei and polar tubes in varying proporti ons, which were reminiscent of sporogonial plasmodia. Conclusions.-The se teratoid structures represent aberrant sporogonial stages, a result of defective maturation in which abnormal cytokinetic replication of organelles occurs, and normal development into uninucleate sporoblasts and spores is inhibited. This leads to the development of teratoid st ages having mature spore walls, but containing multiple sets of nuclei and polar tubes, unusual polyribosomal arrays and vacuoles, or persis tent cleavage. The biological significance of these atypical spores is unknown, but it is evident that they develop in the absence of antimi crosporidian drugs in extraintestinal tissues from nonhuman primates. Teratoid spores of E bieneusi should not be misinterpreted as another microsporidian species or confused with other pathogenic protozoa, nor should their presence be misconstrued as evidence of antimicrosporidi an drug efficacy or toxicity.