Many people have spent a tropical vacation with a bad stomach bug. They might have had dysentery, a painful intestinal infection that is usually caused by bacteria or parasites. Dysentery is defined as diarrhea in which there is blood, pus, and mucous, usually accompanied by abdominal pain. There are two main types of dysentery. The first type, amoebic dysentery or intestinal amoebiasis, is caused by a single-celled, microscopic parasite living in the large bowel. The second type, bacillary dysentery, is caused by invasive bacteria. Both kinds of dysentery occur mostly in hot countries. Poor hygiene and sanitation increase the risk of dysentery by spreading the parasite or bacteria that cause it through food or water contaminated from infected human feces.