The causative agent for amoebiasis, the amoeba [Entamoeba histolytica], exists in two forms. One form is a motile, fragile organism; the other is a nonmotile, resistant cyst. The cysts are present in the infected human colon. The cysts are excreted in the faeces and are swallowed by a new host. In this transmission process the cyst wall is destroyed and new motile organisms are produced. Some of the motile organisms are excreted and die quickly. If the motile organism is not excreted, it attacks the lining of the colon and becomes a cyst. The cyst is not easily destroyed and therefore transmits the infection to other humans, and to animals such as cats and dogs and sometimes pigs. The cysts typically survive in soil for at least 8 days and are not destroyed by the usual concentration of chlorine in purified water. Cysts are destroyed by boiling.
Amoebiasis is transmitted through food and drink containing cysts. Food handlers infected with amoebic cysts are primary transmitters of the disease. Raw vegetables and fruit that are unwashed or that are washed in polluted water and food exposed to flies are also sources of infection. The disease can occur 2 to 4 weeks after exposure to the causative organism or it may not occur for years after exposure.
A mild case of amoebiasis would present symptoms of minor abdominal discomfort with intermittent diarrhoea and constipation. The more serious case would be characterized by fever, chills, and frequent semifluid or fluid stools, which can contain blood or flecks of mucus. The intestinal symptoms may persist for weeks, may come and go, and can result in severe weight loss. In most cases the infection is confined to the intestinal tract but in some cases it spreads and causes hepatitis or a liver abscess. A medical examination is necessary for diagnosis and proper drug therapy. General management includes palliative measures for relief of symptoms and replacement of lost fluid, including blood in some cases.
In 1994 171,000 cases of dysentery with at least 600 deaths were reported in Malawi, Mozambique and Zimbabwe (Holloway 1995).