The problem in Africa

Amoebiasis is caused by the protozoan parasite Entamoeba histiolytica and has a world-wide distribution. It is estimated that 40–50 million cases of amoebic colitis and liver abscess occur annually with 40 000–110 000 deaths (WHO/PAHO/UNESCO, 1997). The infection occurs all over Africa. Transmission is through the faecal–oral route and therefore the infection can flourish whenever sanitation and hygiene is poor. Outbreaks of amoebiasis are frequent during disasters or crises when people are crowded together in refugee camps, after floods and during famine or war.

Organism and life cycle

Entamoeba histiolytica can take two forms: cysts and trophozoites. The cystic form is responsible for transmission from one person to another, but does not have the potential to become invasive and cause disease. Finding cysts in a stool sample therefore, only signifies amoebic infection and does not necessarily indicate amoebic disease. The cysts are shed with the faeces and remain viable for 100 hours at 25 °C under moist conditions (Warhurst, 1999) but much longer in water of lower temperature. Infection of the next person occurs by intake of food or water that is contaminated in which flies often play a role. The cysts can survive gastric acidity so that amoebae can cause infection with a low infective dose (<100 organisms) (Warhurst, 1999). Once in the large intestine, the cysts may release eight trophozoites that are the potentially invasive form which can cause disease. The trophozoites may invade the colonic mucosa causing amoebic colitis or amoeboma; further spread within the portal bloodstream may lead to amoebic liver abscess or abscesses at other sites.