Ultrastructural morphology of Enterocytozoon bieneusi in biliary epithelium of rhesus macaques (Macaca mulatta)

Enterocytozoon bieneusi is the most common microsporidian parasite found in humans with acquired immunodeficiency syndrome. A nearly identical organis m was recently recognized in rhesus macaques (Macaca mulatta). Ultrastructu ral examination of this microsporidian parasite in biliary epithelium of rh esus macaques reveals characteristics unique to E. bieneusi, including 1) a lack of sporophorus vesicles or pansporoblastic membranes, 2) direct conta ct of all stages with the host-cell cytoplasm, 3) elongated nuclei present within proliferative and sporogonial stages, 4) late thickening of the spsr ogonial plasmodium plasmalemma, 5) electron-lucent inclusions present throu ghout the life cycle, 6) precocious development of electron dense discs bef ore plasmodial division to sporoblasts, and 7) the presence of polar tube d oublets within spores and sporoblasts visualized as 5-7 coils in section.