Infectious form of Spironucleus (Hexamita) muris: banded cysts.

Spironucleus muris is a facultative pathogen which may impair experiments on rodents. During examination of thymus-deficient (nu/nu) mice of Han:NMRI stock which were spontaneously infected with this flagellate, infectious cysts were found in the lower intestine and in the faeces. The disease was reproduced in animals fed these cysts. The observed prepatent time was 2-3 days. The cysts are supposed to be the only infectious form of S. muris. The immature and mature stages, of the cyst with a characteristic banded appearance ('Easter-egg cysts') are described. The description of the cystic form of S. muris in the faeces of infected mice makes possible the diagnosis of spironucleosis without sacrificing the host.