Cause
Amebiasis is caused by Entamoeba histolytica, an ameba that predominantly infects humans.
This protozoan has a relatively simple life cycle consisting of two stages, the dormant cyst and the vegetative trophozoite stage. The main mode of transmission of amoebiasis is ingestion of E. histolytica cysts from contaminated food or water. Excystation in the intestinal lumen produces trophozoites that colonize the large intestine where they spread and encyst. Cysts are excreted in stools and perpetuate the life cycle by further faecal-oral spreading
Amoebiasis is particularly common in regions and countries with defective sanitation, where ameba parasites can spread easily. This neglected disease is a major public health issue in these areas, and the effective diagnosis of cysts and preventive measures of hygiene are vital in tackling the problem.
Symptoms
Although infection does not generally lead to symptoms, is some cases for unknown reasons, trophozoites are invasive and destroy the intestinal mucosa causing painful, bloody diarrhea (amebic dysentery), ulcers, and in the most severe cases leading to abscesses in the liver, lungs, and brain
Epidemiology
Between 10 and 20% of infected people may develop severe symptoms. The disease is responsible for 40,000 to 100,000 deaths each year, mainly in poorest regions of South-East Asia, South-Eastern and Western Africa, and Central and South America, where the hygiene conditions and the lack of effective sewage treatment plants encourage the spread of amebae. In some regions of India, Mexico, Bangladesh, and South Africa, up to 20% of the population can be infected. In developed countries the disease is rarer, with sporadic cases in travelers returning from endemic areas.
Treatment
Acute amoebiasis is treated by taking a broad-spectrum antiparasitic drug combined with amoebicides of contact acting locally in the gut lumen. In areas where amoebiasis is endemic, WHO also recommends treating asymptomatic carriers with contact agents to reduce the risk of transmission.
Although the antiparasitic drugs currently available are known to be effective, the use of such drugs, nonspecific, raises the problem of development of new resistance in the targeted pathogen.
Prevention, to reduce the transmission of cysts, remains essential. It is based primarily on the elimination of faecal contamination of water, food and hands as well as the development of diagnostic methods to identify cysts, even in asymptomatic carriers.