Entamoeba Suis

Synonym: Entamoeba debliecki, pro parte.

A number of authors have used the name, Entamoeba polecki Prowazek, 1912, for this species, but this name must be considered a nomen nudum because Prowazek's description was so poor as to be unrecognizable (see Hoare, 1940, 1959).

E. suis occurs in the cecum and colon of swine. Chang (1938) found it in 71% of 209 pigs in China. Pavloff (1935) found it in 26 of 1840 pigs in France and Bulgaria. Simitch et al. (1959) found it in 8% of 1800 pigs in Yugoslavia. Frye and Meleney (1932) found it in 63% of 80 pigs, Alicata (1932) found it in 43% of 35 pigs, and Noble and Noble (1952) found it in all of 30 pigs in the United States. Mackinnon and Dibb (1938) found it in the European wild boar (Sus scrofa), giant forest hog (Hylochoerus meinertzhageni) and Indian boar (Sus cristatus) in a London zoo. Kessel and Johnstone (1949) and Kessel and Kaplan (1949) reported "E. polecki" from the rhesus monkey but remarked that it appeared identical with E. chattoni of monkeys; this is the species to which their form should be assigned. Ten human infections have been reported (Kessel and Johnstone, 1949; Lawless, 1954; Burrows and Klink, 1955). However, altho no human cross-infection experiments have been attempted, E. suis does not seem to be readily transmissible to man. Chang (1939) observed that it was not present in 27 Chinese butchers, altho their methods of slaughtering provided ample opportunity for infection. Pavloff (1935) was unable to infect kittens with it by intrarectal inoculation.

E. suis has been described by a number of authors, including Noble and Noble (1952) in domestic animals, and by Burrows (1959) in man. The following description is based on Noble and Noble. The trophozoites are 5 to 25 u long. Some authors (e.g., Hoare, 1959; Simitch et al. 1959) have considered the small forms to be a separate species, E. debliecki, but such a separation does not appear to be justified.

The nucleus varies in appearance. The endosome is central and is usually quite large. It may sometimes almost fill the nucleus, but it may also sometimes be small and similar to that of E. histolytica. There is a rather homogeneous ring of peripheral chromatin within the nuclear membrane. There are ordinarily no chromatin granules between the endosome and the peripheral ring. The cytoplasm is granular and vacuolated, and contains bacteria in its food vacuoles. The cysts are 4 to 17 u in diameter and have a single nucleus when mature. The chromatoid bodies in the cysts vary markedly in shape from stout rods with rounded ends similar to those of E. histolytica to irregular granules of varying size. There may or may not be a glycogen vacuole. Cysts without chromatoid bodies or glycogen vacuoles are also common.

E. suis is probably non-pathogenic. Smith (1910) found amoebae in sections of intestinal ulcers in swine. Hartmann (1913), who studied Smith's preparations, named the amoeba E. suis. Ratcliffe (1934) observed amoebae associated with necrosis in sections of the colon of pigs which had died of experimental hog cholera. However, altho E. suis is very common in swine, it has never been found in sections of intestinal lesions of hundreds of swine examined by University of Illinois pathologists.

E. suis can be cultivated in the usual media. It is apparently less sensitive than E. histolytica to amoebicidal drugs, but Frye and Meleney (1932) eliminated it from pigs by feeding 50 mg/kg carbarsone in the milk daily for 10 days.