Synonyms: Amoeba limax, Entamoeba nana, Endolimax intestinalis, Endolimax cynomolgi, Endolimax suis, Councilmania tenuis.
Hosts: Man, pig, gorilla, chimpanzee, gibbon, macaques and other monkeys and baboons, including Macaca mulatta, M. irus, M. sinica, M. sancti-johannis, M. lasiotis, M. philippinensis, Papio papio, Cercocebus aethiops, Cercopithecus ascanius, Gamadrillus sp., and Erythrocebus patas (see Mackinnon and Dibb, 1938). These authors also reported a morphologically indistinguishable form from the capybara (Hydrochoerus capybara) and tree porcupine (Coendou prehensilis).
It is quite likely that E. ratti (see below) may be a synonym of E. nana, so that the latter's host range may be even broader than that given above. Chiang (1925) considered E. ratti a separate species because he was unable to infect 14 rats with E. nana from man. However, Kessel (1928) succeeded in doing so, and Smith (1928) found an E. nana-like amoeba in 4 of 63 rats which had been fed human feces but did not know whether it had already been present in the rats.
Dobell (1933) transmitted E. nana from Macaca sinica to a man (himself) and from man to M. mulatta. Kessel (1928) infected M. irus with E. nana from man. However, Simitch et al. (1959) were unable to infect 4 young pigs with E. nana from man and consequently named the pig form E. suis; they gave no details of their experiments.
Location: Cecum, colon. Hegner (1929) and Dobell (1933) found E. nana in the vagina of macaques, where it was most likely of fecal origin.
Geographic Distribution: Worldwide.
Prevalence: E. nana is common in man. According to Belding (1952), it was found in 20.5% of 18,333 persons in 20 surveys thruout the world and in about 14% of those examined in the United States. Frye and Meleney (1932) found it in 5.5% of 127 pigs in Tennessee, Alicata (1932) found it in 1 of 35 pigs in the U.S., Kessel (1928) found it in 14% of the pigs examined by him in China, and Chang (1938) found it in 15% of 209 pigs in China. Simitch et al. (1959) found it in 8% of 1800 pigs in Yugoslavia.
Morphology: The trophozoites are 6 to 15 u in diameter with an average of 10 u. They move sluggishly by means of a few blunt, thick pseudopods. The endoplasm is granular, vacuolated and contains bacteria and crystals. The nucleus contains a large, irregular endosome composed of a number of chromatin granules. Several achromatic fibrils run from the endosome to the nuclear membrane. There are ordinarily no peripheral chromatin granules, but Stabler (1932) noted that they are formed after fixation in Schaudinn's fluid containing 20% acetic acid. The cysts are oval, often irregular, and thin-walled; they are usually 8 to 10 u long but may range from 5 to 14 u. The mature cysts contain 4 nuclei, and they may contain ill-defined glycogen bodies. They have no chromatoid bodies but may have small granules resembling volutin and occasionally a few filaments of uncertain nature.
Life Cycle: Reproduction is by binary fission in the trophozoite stage. The amoeba which leaves the cyst is multinucleate, but it divides into uninucleate amoebulae which grow into ordinary trophozoites.
Pathogenesis: E. nana is non-pathogenic.
Bionomics and Epidemiology: E. nana is transmitted in the same way as other enteric amoebae. Dobell (1933) found that its cysts could live at least 2 weeks at room temperature (15-24° C) and at least 3 weeks at 10° C, while all the trophozoites died in 24 hours at both temperatures. Frye and Meleney (1932) found E. nana cysts in 1 out of 46 lots of flies which they examined in Tennessee.
Cultivation: This species can be cultivated in the usual media.
Treatment: Little is known about the treatment of E. nana. Dobell (1933) and others found that emetine has no effect on it.
Prevention and Control: The same preventive measures recommended for E. histolytica will also prevent E. nana infections.