PROTOZOAN INFECTIONS Amoebiasis The amoebae are a class of protozoans that move by amoeboid movement and eat by phagocytosis. They can simply be termed ‘blobs’ of protoplasm. They are very common organisms, found free in nature in damp and wet habitats. Only one is associated commonly with human disease – Entamoeba histolytica. This organism usually causes amoebic dysentery and remains in the intestine for the duration of the infection. It can remain even after the symptoms of diarrhoea have gone. The patient is then a carrier and can transmit the amoebae via the faecal/oral route to infect other individuals. It has been estimated that the carrier rate could be more than 50 per cent in poorly sanitised areas of the world. From carriers, the amoeba is excreted in an encysted form, which is infective. In acute diarrhoea, however, the organism is excreted as a motile trophozoite, which causes infections only rarely owing to its short life outside the gastrointestinal tract. Occasionally, the organism causes perforation of the muscular coat of the intestine. The organism can then gain access to the hepatic portal system and spread throughout the body, causing abscesses, principally in the liver and lungs. Various other amoebae can cause gastrointestinal infections and some occur as commensals in the intestines.