This species, which may be a synonym of E. nana, occurs in the cecum and colon of laboratory and wild rats. Andrews and White (1936) found it in 1 out of 2515 wild rats in Baltimore, and Baldassari (1935) found it in 1 of 225 wild rats in Toulon, France. Chiang (1925) did not describe it, but merely stated that it was morphologically identical with E. nana.
This species occurs commonly in the cecum of the guinea pig. Hegner (1926) found it in Baltimore and Hegner and Chu (1930) found it in the Philippines. Nie (1950) found it in 18% of 84 guinea pigs in Pennsylvania. It is somewhat smaller than E. nana, the trophozoites measuring 5 to 11 by 5 to 8 u, but otherwise resembles it. Nie saw one specimen with an ingestion tube. The cysts are apparently unknown.
Synonyms: Pygolimax gregariniformis, Endolimax janisae, Endolimax numidae.
This species is found in the ceca of the chicken, turkey, guinea fowl, pheasant, domestic goose, domestic duck and various wild birds, including the black duck (Anas rubripes tristis), black-crowned night heron (Nycticorax nycticorax) and screech owl.
E. gregariniformis was first described by Tyzzer (1920) from the turkey; he transmitted it easily to the chicken. Hegner (1926) described it from the chicken, naming it E. janisae. Hegner (1929a) found the same species and another form which he named E. numidae in the guinea fowl. The latter was smaller than E. gregariniformis, averaging 4 by 3 u, but nevertheless fell within its size range and did not differ from it morphologically. Hegner (1929a) infected chicks with both sizes of Endolimax from the guinea fowl and also with Endolimax from the domestic goose, domestic duck and screech owl. Richardson (1934) infected chicks with Endolimax from the duck, goose, pheasant, black duck and black-crowned night heron.
E. gregariniformis occurs thruout the world and is non-pathogenic. McDowell (1953) found it in over 50% of a large number of chickens he examined in Pennsylvania.
The trophozoites of E. gregariniformis are usually 4 to 13 u long with a mean of 9 by 5 u, altho Hegner (1929a) found a small race in the guinea fowl. The trophozoites are oval, often with a posterior protuberance, and move sluggishly. The ectoplasm is not clearly separated from the endoplasm. The food vacuoles contain bacteria. The nucleus is very similar to that of E. nana but tends to have a larger endosome and a more apparent nuclear membrane, often with chromatin granules at the juncture of the achromatic threads with the membrane. The cysts have 4 nuclei when mature; they measure 7 to 8 by 8 to 11 u with a mean of 10 by 7 u (McDowell, 1953). They tend to be somewhat lima bean-shaped instead of truly ovoid, and are often highly vacuolated.