Synonyms: Amoeba muris, Councilmania muris, Councilmania decumani.
E. muris occurs commonly in the cecum and colon of rats, mice and the golden hamster thruout the world. Andrews and White (1936) found it in 10.4% of 2515 wild rats in Baltimore. Fry and Meleney (1932) found it in 48% of 48 wild Rattus norvegicus and 24.1% of 54 grey mice captured in a rural area of Tennessee. Tsuchiya and Rector (1936) found it in 8% of 100 rats in St. Louis. Elton, Ford and Baker (1931) reported it in 50% of 440 long-tailed field mice (Apodemus sylvaticus), 41% of 116 bank voles (Clethrionomys glareolus) and 41% of 51 short-tailed field mice (Microtus hirtus) in England. Wantland (1955) found it in 33% of 412 golden hamsters from several American suppliers and laboratories. Mudrow-Reichenow (1956) found E. muris in 7% of 14 golden hamsters, 35% of 21 laboratory rats and 39% of 92 laboratory mice in Germany.
Kessel (1924) transmitted E. muris from the rat to the mouse and vice versa. Neal (1947, 1950a) and Saxe (1954) infected rats with E. muris from the golden hamster and mouse. Saxe (1954) infected the golden hamster with E. muris from the rat.
E. muris is morphologically similar to E. coli. Its trophozoites are 8 to 30 u long. Its cysts are 9 to 20 u in diameter and have 8 nuclei when mature. Its nuclear structure and division were studied by Wenrich (1940). He found that the nucleus is intermediate in structure between those of E. histolytica and E. coli but more nearly resembles the latter. It varies in diameter from 3 to 9 u with a mean of 4 to 5 u. In division, approximately 8 chromosomes are formed. Binucleate cysts almost always contain a large glycogen vacuole, and mononucleate cysts very frequently do.
E. muris is non-pathogenic. It is important to the research worker because it must be differentiated from other amoebae introduced in experimental infections.
This species is often referred to as Entamoeba cobayae (Walker, 1908) Chatton, 1917. However, the form which Walker (1908) called Amoeba cobayae was seen in cultures from a guinea pig intestine and was not an Entamoeba at all. Hoare (1959) considered this species a synonym of E. muris.
E. caviae is common in the ceca of laboratory guinea pigs. Nie (1950) found it in 14% of 84 guinea pigs in Pennsylvania and Mudrow-Reichenow (1956) found it in 46% of 13 guinea pigs in Germany.
E. caviae resembles E. coli. Its morphology has been studied by Nie (1950). The trophozoites are 10 to 20 u in diameter with a mean of 14.4 u. The nucleus is 3 to 5 u in diameter. Its endosome varies in size and shape and may be central or eccentric. In some cases it is composed of several granules. There is a ring of coarse chromatin granules inside the nuclear membrane. The cysts are 11 to 17 u in diameter with a mean of 14 u and have 8 nuclei (Holmes, 1923). They are rare.
E. caviae is non-pathogenic. Because it is so common, it must be differentiated from other amoebae in experimentally infected animals.
This species occurs in the cecum and colon of the domestic rabbit. It is not pathogenic. It resembles E. coli, and Kheisin (1938) has even suggested the name Entamoeba coli forma cuniculi for it. Hoare (1959) considered it a synonym of E. muris. It is apparently quite common in rabbits, altho there seem to be relatively few reports on it. Kheisin (1938) found it in 25% of the rabbits he examined in Russia. The trophozoites range from 12 to 30 u in length with means of 13 to 17 u in different rabbits. The cysts have 8 nuclei. They range in diameter from 7 to 21 u. with means of 10 to 15 u in different rabbits.