Gastrointestinal Amebiasis by Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite that causes intestinal and extraintestinal infections in humans. It belongs to the phylum Sarcomastigophora, subphylum Sarcodina, class Lobosa, order Amoebida, and family Entamoebidae. It has two main forms: the cyst and the trophozoite.

The cyst is the infectious form that can survive in the external environment and is transmitted by fecal-oral route through contaminated food, water, or objects. The cyst is round or oval, measuring 10 to 16 micrometers in diameter, and has a thick wall that protects it from harsh conditions. The cyst contains one to four nuclei, depending on its stage of development. The mature cyst has four nuclei and can be distinguished from other similar parasites by its chromatoid bodies, which are rod-shaped structures with blunt ends.

The trophozoite is the vegetative form that lives and multiplies in the human colon. It is responsible for causing disease and tissue damage. The trophozoite is motile and moves by extending pseudopods (false feet). It measures 10 to 50 micrometers in diameter and has a single nucleus with a central karyosome (a mass of chromatin) and peripheral chromatin granules. The trophozoite feeds on bacteria, red blood cells, and host tissues by phagocytosis (engulfing). It can also secrete enzymes and toxins that lyse the cells and cause inflammation.

Entamoeba histolytica is a pathogenic species that can cause amoebic dysentery, amoebic colitis, amoebic liver abscess, and other extraintestinal complications. It can invade the intestinal wall and reach the bloodstream, where it can spread to other organs such as the liver, lungs, brain, or skin. Entamoeba histolytica can be distinguished from other nonpathogenic species of Entamoeba, such as Entamoeba dispar or Entamoeba moshkovskii, by molecular or antigenic tests.