Dysentery an enteric illness caused by pathogenic bacteria or parasitic protozoa. Bacterial dysentery is also called bacillary dysentery because the pathogen is a bacillus or rod-shaped bacterium. Since the dysentery causing bacteria belong to the genus Shigella, the dysentery is also called shigellosis. Parasitic dysentery is caused by the amoeba Entamoeba histolytica and is also known as amoebiasis.

Dysenteric illness can be acute or chronic. Bacillary dysentery is mostly an acute infection triggered by ingestion of the Shigella bacillus through contaminated food or water. Poor personal hygiene and public sanitation facilitate the spread of the disease. The Shigella bacillus multiplies in the intestine, invades the epithelial cells of the mucosal lining causing extensive tissue damage, resulting in inflammation and bleeding, and causing fever and severe abdominal pain. Stool mixed with shed mucus and blood is characteristic of bacillary dysentery and is passed frequently with characteristic painful defecation. Amoebic dysentery, on the other hand, is not usually associated with bloody stool and usually is a less severe disease. Frequent stool with mucous and abdominal pain is the major clinical manifestation of amoebic dysentery. In some patients, amoebic dysentery tends to be chronic and lasts for months which probably is the result of repeated re-infection due to exposure to unhygienic conditions.

Both bacillary dysentery and amoebic dysentery are highly endemic in Bangladesh and is the cause of extensive morbidity and mortality, particularly in children with attacks of bacillary dysentery. Explosive epidemics of bacillary dysentery occur every year often spreading rapidly; however, amoebic dysentery spreads less rapidly. Approximate yearly cases of bacillary dysentery in Bangladesh in a typical year is estimated to be between 2,00,000 and 3,00,000 while the number for amoebic dysentery is estimated to be between 25,000 and 50,000.

Amoebiasis is commonly known as amoebic dysentery. The unicellular pathogen invades the target tissue, intestinal mucosa, and upon establishment of the disease results in the formation of discrete ulcers in the mucosa from which mucus, necrotic cells and live amoeba cells are discharged. Clinical symptoms of the disease include abdominal pain and frequent passage of stool with mucous (30 or more movements in a day), painful defecation, nausea, vomiting and general incapacitation. Unlike bacillary dysentery which is caused by bacteria and of which the discharge of fresh blood with stool is a common manifestation, in amoebiasis the stool usually does not contain any blood except in very severe cases.

Incidence of amoebiasis is high where sewerage system is poor and in villages of developing countries where open air defecation is common. The cysts of the parasite commonly find entry into the human intestine through contaminated vegetables that are eaten raw such as components of salad, and with vegetables that have not been adequately cooked. Individuals who carry the parasite but do not develop overt symptoms of the disease are called asymptomatic carriers. They may also spread the parasite by contaminating food handled in unhygienic manner and presumably also by person to person contact.

The poor socio-economic condition of Bangladesh and the practice of unsafe faeces disposal and, in villages, the practice of open-air defecation, have made amoebiasis an endemic disease of high prevalence throughout the year. It thus constitutes a major public health problem for the country. Asymptomatic carriers may often transit into episodes of full-blown illness which is influenced by factors such as malnutrition and other stress conditions. High carbohydrate and a low protein containing diet is known to favour development of the disease both in experimental animals and in humans. In many developing countries including Bangladesh, malnutrition involving both carbohydrate and protein deficiency is common. Thus, the large malnourished population of the country is particularly vulnerable to amoebic dysentery. A common extra-intestinal metastatic manifestation of amoebiasis is amoebic hepatitis, commonly called liver abscess, which is also common in amoebic patients in Bangladesh. [Zia Uddin Ahmed]