People can become infected after ingesting water or food contaminated with somebody’s excreted parasites. It is uncommon except in developing countries in the world's tropical zones, where it is very prevalent. In the vast majority of cases, amoebiasis causes no symptoms – only 10% of infected individuals become ill. The amoeba can exist for long periods of time in the large bowel (colon). Intestinal amoebiasis is caused by a protozoan parasite, Entamoeba histolytica. If one person has bacillary dysentery, others at their home, daycare, school, or nursing home are at risk of infection from close contact with the infected individual. Young children (ages 1 to 5) living in poverty are most likely to contract shigellosis, campylobacteriosis, or salmonellosis. If people live or travel in an area where poverty or overcrowding may interfere with good hygiene and sanitation, they are at risk of being exposed to invasive bacteria. Both infections are spread by ingestion of food or water contaminated with infected feces.
They penetrate the lining of the intestine, causing swelling, ulcerations, and severe diarrhea containing blood and pus. The Shigella and Campylobacter bacteria that cause bacillary dysentery are found all over the world. Dysentery is rarely caused by chemical irritants or by intestinal worms.
The frequency of each pathogen varies considerably in different regions of the world. coli, and Salmonella species of bacteria. These infections include Shigella, Campylobacter, E. Bacterial infections are by far the most common causes of dysentery.