FURTHER OBSERVATIONS ON THE ULTRASTRUCTURE OF SEPTATA-INTESTINALIS CALI, KOTLER AND ORENSTEIN, 1993

A microsporidium, identified as Septata intestinalis Call, Kotler and Orenstein, 1993, has been studied by light and electron microscopy fro m four patients with the acquired immunodeficiency syndrome (AIDS) in Sydney, Australia. The parasite was found in small intestinal and colo nic enterocytes and lamina propria macrophages, urine, and in nasal ep ithelium, the last being a site of infection not previously reported f or the species. Ultrastructurally it resembles species of Encephalitoz oon in that it develops in host cells within parasitophorous vacuoles, with meronts and sporonts dividing mainly by binary fission, the mero nts lying adherent to the vacuolar membrane and sporogonic stages free in the lumen. The microsporidium has additional features which are di stinctive: the vacuole is lobed and the sporogonic stages that it cont ains are separated by septa that condense from a granular matrix with additions from host cell cytoplasmic debris derived by coalescence of vacuoles. The parasitophorous vacuole membrane is present throughout d evelopment, even around isolated meronts and the matrix is evenly dist ributed in vacuoles containing only meronts. Tubular structures appare ntly arising from the outer coat of sporonts and sporoblasts run throu gh the vacuole. On the basis of these results, it is suggested that th e description of the genus Septata is modified to state that the entir e development is within parasitophorous vacuoles and that sporogony is mainly disporoblastic. These being characters of the genus Encephnlit ozoon, gene sequencing will be required further to evaluate the relati onship of the two genera.