Tritrichomonas muris in the hamster: pseudocysts and the infection of newborn.

Female golden hamsters, either in the last week of pregnancy or in the first weeks of nursing, excreted in their feces variable numbers of pseudocysts of Tritrichomonas muris. Pseudocysts examined by electron microscopy had internalization of the 3 anterior flagella and the undulating membrane with its recurrent flagellum. The undulating membrane and the associated marginal lamellae were characteristic of T. muris. Pseudocysts gradually become motile after 2 or more hours of incubation in medium. The "excysted" trophozoites were identified ultrastructurally as T. muris. Newborn hamsters were not infected with T. muris at 3 days of age, but by the 7th day essentially all were found to have infected ceca, concomitant with cecal enlargement and the appearance of adult-type feces.