Dysentery is an infectious disease of the colon that is characterized by severe and bloody diarrhea, abdominal pain, fever and dehydration.

The term “dysentery” refers specifically to the bloody diarrhea that is its most common symptom. Since the late 1800s, physicians have identified two types of dysentery. The most common is bacillary dysentery, which is caused by Shigella bacteria. It is also called shigellosis. The other type is amebic dysentery, which is caused by the parasitic amoeba Entamoeba histolytica. It is also called amebiasis. The severity of the dysentery caused by each type of microbe may differ. People with shigellosis may experience mild or severe cases. Most people with amebiasis experience no symptoms at all and may unknowingly carry the parasite for years.

Dysentery has been known to humanity since its early recorded history. It commonly occurs under circumstances of overcrowding and poor sanitation, such as war, natural disasters or unhygienic living conditions. For example, thousands of soldiers died of dysentery during the American Civil War and World War I.

Cases of dysentery occur worldwide, but are more common in developing countries and in tropical areas with poor sanitation, such as Africa, Latin America, Southeast Asia and India. In the United States, outbreaks occur in crowded settings such as day care centers or institutions and from instances of unsanitary food handling or contaminated water.

The organisms that cause both types of dysentery are present in the stools of infected people. They can be spread in several ways:

• Person-to-person contact. A person with dysentery can transmit the microbes to another individual from their fecal matter. This can happen with improper hygiene or handwashing after a bowel movement. Dysentery can also be spread during anal sexual contact.
  
  
• Eating contaminated food. Dysentery can be spread when contaminated food or water is ingested. Food can become contaminated by infected food handlers who do not wash their hands or when it is harvested from fields contaminated or fertilized with sewage. It can also be spread by infected flies or cockroaches that come into contact with food.
  
  
• Drinking or swimming in contaminated water. Water can become contaminated with sewage or when someone with dysentery bathes or swims in it.

When the organisms enter the body, they invade the cells lining the large intestine and multiply. They then produce the bloody, mucus-laden diarrhea that characterizes dysentery.

The effects of dysentery vary, usually depending on the overall health of the infected individual. Infants, young children and elderly people are most severely infected by the condition. People with compromised immune systems such as patients with acquired immunodeficiency syndrome (AIDS) are also more susceptible to severe cases of dysentery. The most common complication for these groups is the potential for dehydration as a result of the diarrhea. Lack of adequate medical care and attention to dehydration can make dysentery a fatal disease, especially in developing countries.

Additional complications may occur when dysentery toxins reach other body systems. Patients with shigellosis, especially children, are susceptible to secondary bacterial infections of the blood and kidneys. Shigellosis patients with a specific gene are more likely to develop Reiter’s syndrome that may include arthritis (joint inflammation) and possibly inflammation of the  urinary tract and eyes. In people with amebiasis symptoms, the disease may spread from the large intestine to the liver, where it may cause abscesses. It may also eventually spread to the lungs and other organs.

About 18,000 cases of shigellosis are reported to the Centers for Disease Control and Prevention (CDC) each year. However, experts believe the number of cases may be much higher because patients who experience mild symptoms do not seek treatment and are not diagnosed. The U.S. Food and Drug Administration (FDA) estimates that there may be as many as 300,000 cases each year in the United States.