Synonym: Entamoeba polecki, pro parte.
This species occurs in the large intestine of macaques and a number of other monkeys. It was first seen by Chatton (1912), who called it Loeschia sp., and was given its present name by Swellengrebel (1914), who found it in the rhesus monkey. This name was thought to be one of the many synonyms of E. histolytica until Salis (1941) showed that it was not. Kessel and Johnstone (1949) found E. chattoni and E. polecki to be morphologically similar, and used the older name, E. polecki, for the species. However, in the absence of cross-infection experiments between pigs and monkeys, it is best to retain the name, E. chattoni, for the monkey form. In any case, E. polecki is a nomen nudum and should be replaced by E. suis. The proper name for the forms in the 10 human cases which have been reported (see Burrows and Klink, 1954) is uncertain. Perhaps it should depend in each case on the source of infection, whether pig or monkey, or perhaps both these names will eventually be dropped in favor of E. bovis. However, for the present E. chattoni is preferable.
E. chattoni is probably much more common in monkeys than E. histolytica, from which it must be distinguished. Mudrow-Reichenow (1956) found it in 6 of 7 rhesus monkeys in Germany. The trophozoites of E. chattoni are 9 to 25 u long. The cysts are 6 to 18 u in diameter. Salis described two size races with cysts averaging 10.9 and 13.1 u, respectively but other workers have not made this differentiation. The nucleus varies a great deal in morphology. It may be indistinguishable from that of E. histolytica, with a small, central endosome and a row of fine, peripheral chromatin granules.
On the other hand, the endosome may be large or small, central or eccentric, compact or diffuse, and composed of one to many granules, while the peripheral chromatin may be fine or coarse, uniform, irregular or diffuse, and there may or may not be chromatin granules between the endosome and the peripheral chromatin. The cysts are almost always uninucleate when mature. Less than 1% are binucleate, and they are never tetranucleate. The chromatoid bodies are usually irregular and small, but may also be rod-shaped with round or pointed ends, oval or round. A glycogen vacuole may or may not be present.
E. chattoni is generally considered non-pathogenic, altho 2 of the human patients studied by Burrows and Klink (1955) had diarrhea which may or may not have been caused by the amoebae.
Noble (1955) found this species in the feces of 12 of 15 carabao (Bubalus bubalis) from several islands in the Philippines. Only 2 trophozoites were seen. They averaged 12 u in diameter. The cysts are 5 to 9 u in diameter with a mean of 8 u. They contain 1 or more vacuoles, but usually a single large one which crowds the cyst contents to its periphery. The chromatoid bodies are usually small and irregular in shape but may occasionally be large, with rounded ends, similar to those of E. histolytica. The cysts contain a single nucleus 2.6 u in diameter with a large endosome 1.4 u in diameter which often appears to be a cluster of 4 granules. There is usually a distinct peripheral ring of chromatin, but the amount of peripheral chromatin may vary from practically none to a ring of dots to a few isolated clumps. There is no periendosomal chromatin. Noble (1955) considered E. bubalus to differ from other entamoebae with uninucleate cysts in the character of its nucleus - the heavy, usually uniform outer ring of chromatin and the large, prominent endosome.