Abstract
The structure of the spores of Encephalitozoon cuniculi Levaditi, Nicolau & Schoen, 1923, shows that it belongs to the Order Microsporidia Balbiani, 1882 and that the genus Encephalitozoon is a synonym for the older Nosema Nägeli, 1857. Therefore, the species of Microsporidia described from mammals are now: Nosema cuniculi (Levaditi, Nicolau & Schoen, 1923), Nosema rabiei (Manouelian & Viala, 1924) and Nosema chagasi (Torres, 1927). Another microsporidian in mammals is Thelohania apodemi (Doby, Jeannes & Rault, 1963).