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 from four patients with the acquired immunodeficiency syndrome (AIDS) in Sydney, Australia. The parasite was found in small intestinal and colonic enterocytes and lamina propria macrophages, urine, and in nasal epithelium, the last being a site of infection not previously reported for the species. Ultrastructurally it resembles species of Encephalitozoon in that it develops in host cells within parasitophorous vacuoles, with meronts and sporonts dividing mainly by binary fission, the meronts lying adherent to the vacuolar membrane and sporogonic stages free in the lumen. The microsporidium has additional features which are distinctive: the vacuole is lobed and the sporogonic stages that it contains 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 development, even around isolated meronts and the matrix is evenly distributed in vacuoles containing only meronts. Tubular structures apparently arising from the outer coat of sporonts and sporoblasts run through the vacuole. On the basis of these results, it is suggested that the description of the genus Septata is modified to state that the entire development is within parasitophorous vacuoles and that sporogony is mainly disporoblastic. These being characters of the genus Encephnlitozoon, gene sequencing will be required further to evaluate the relationship of the two genera.