Entamoeba histolytica

Abstract

Entamoeba histolytica is a protozoan parasite of the human colon. Motile trophozoite forms invade the bowel wall and also inhabit the lumen. The trophozoites are capable of undergoing encystment within the bowel lumen and may then be shed in the faeces. It is these cysts which are implicated in further transmission as a result of the consumption of contaminated water or vegetables. After ingestion, cysts pass through the stomach to reach the small intestine, where they can transform into the trophozoite form. The organism adheres to the intestinal mucosa by means of specific receptors and produces cytotoxic factors which result in the characteristic inflammation and ulceration of the gut wall. The range of illness which may result is very wide, ranging from asymptomatic carriage, through diarrhoeal illness which may be chronic and mild in nature, more severe dysenteric illness with fever and severe abdominal pain, to severe massive infection with perforation of the gut and amoebic peritonitis or the development of toxic megacolon. Extraintestinal infection can occur, and most commonly involves the liver, although the lungs and rarely the brain and other sites may be involved.