Genus Iodamoeba

In this genus the nucleus is vesicular, with a large endosome rich in chromatin, a layer of lightly staining globules surrounding the endosome, and some achromatic strands between the endosome and nuclear membrane. The cysts contain a large glycogen body which stains darkly with iodine. They are ordinarily uninucleate. This genus occurs in vertebrates. A single species is recognized.

Iodamoeba Buetschlii

Synonyms: Entamoeba williamsi pro parte, Endolimax williamsi, Endolimax pileonucleatus, lodamoeba wenyoni, lodamoeba suis, Endolimax kueneni.

Hosts: Pig, man, chimpanzee, gorilla, macaques and other monkeys and baboons, including Macaca mulatta, M. irus, M. sancti-johannis, M. lasiotis, M, philippinensis, Cercocebus aethiops, Cercopithecus mona, C. ascanius, Papio papio, kra monkey, green monkey, Anubis baboon, Gelada baboon and mandrill, (Mackinnon and Dibb, 1938; Wenrich, 1937). In addition, Mackinnon and Dibb (1938) found this species in the giant forest hog, Hylochoerus meintritz-hageni. Smith (1928) infected rats with I. buetschlii from man, and Pavloff (1935) did so with a strain from the pig. However, Simitch et al. (1959) were unable to infect man with cysts from fresh pig feces or to infect the pig with cysts from fresh human feces; they gave no details of their experiments.

Location: Cecum and colon.

Geographic Distribution: Worldwide.

Prevalence: I. buetschlii is the commonest amoeba of swine, and the pig was probably its original host. Frye and Meleney (1932) found it in 24% of 127 pigs in Tennessee. Alicata (1932) found it in 25% of 35 pigs in the U.S. Cauchemez (1921) estimated that it was present in 50 to 60% of the pigs he examined in France. Noller (1922) found it in about 20% of those he examined in Germany. Pavloff (1935) found it in 29% of 530 pigs in France and 30% of 1310 pigs in Bulgaria. Simitch et al. (1959) found it in 8% of 1800 pigs in Yugoslavia. Kessel (1928a) found it in 42% of the pigs he examined in China, and Chang (1938) found it in 51% of 209 pigs in China.

According to Belding (1952), I. buetschlii was found in 8.4% of 17,568 persons in 20 surveys thruout the world, and in 4% of the people in American surveys. Wenrich (1937) found it in 44% of 55 apes and monkeys which he examined.

Morphology: Wenrich (1937), among others, has studied the morphology of I. buetschlii. The trophozoite is usually 9 to 14 u long but may range from 4 to 20 u. It has clear, blunt pseudopods which form slowly, and it moves rather slowly. The ectoplasm is clear, but not well separated from the granular endoplasm. Food vacuoles containing bacteria and yeasts are present in the cytoplasm. The nucleus is relatively large, and ordinarily contains a large, smoothly rounded, central endosome surrounded by a vesicular space containing a single layer of periendosomal granules about midway between the endosome and the nuclear membrane. Fibrils extend to the nuclear membrane, but there are no peripheral granules inside the membrane. Stabler (1945) described tube-like processes which may be used for feeding in 12% and 27%, respectively, of the trophozoites of 2 human strains.

The cysts are often irregular in form. They are usually 8 to 10 u long, but may range from 5 to 14 u. They contain a single nucleus in which the periendosomal granules have usually aggregated into a crescent-shaped group at one side of the endosome, pushing it to one side. They contain a large, compact mass of glycogen which stains deeply with iodine. The glycogen disappears after 8 to 10 days in feces held at room temperature, and at the same time the cysts die and disintegrate (von Brand, 1932). There are no chromatoid bodies in the cysts, but they may contain small, deeply staining granules something like volutin granules.

Life Cycle: I. buetschlii reproduces by binary fission. Pan (1959) studied nuclear division in the trophozoites. He considered the process unique; his paper should be read for the details. The haploid number of chromosomes is usually more than 10 - possibly 12.

Pathogenesis: I. buetschlii is non-pathogenic except under unusual circumstances. These have never been noted in the pig, but Andrew (1947) reported symptoms similar to those of chronic E. histolytica in a few persons, and Derrick (1948) described a fatal generalized infection in a Japanese soldier captured in New Guinea in which there were ulcers in the stomach, small intestine, large intestine, lymph nodes, lungs and brain.

Bionomics and Epidemiology: I. buetschlii, like other intestinal amoebae, is transmitted by cysts.

Cultivation: This species can be cultivated in the usual media.

Treatment: Little is known about treatment for I. buetschlii, but it can be eliminated by emetine.

Prevention and Control: The same preventive measures recommended for E. histolytica will also prevent I. buetschlii infections.