Water-Borne Diseases: Cholera and Dysentery
Dysentery is an inflammation of the intestine characterized by the frequent passage of feces with blood and mucus. Like cholera, dysentery is spread by fecal contamination of food and water, usually in impoverished areas with poor sanitation. Epidemics are common in these areas. A four-year epidemic in Central America, starting in 1968, resulted in more than 500,000 cases and more than 20,000 deaths. Since 1991, dysentery epidemics have occurred in eight countries in southern Africa (Angola, Burundi, Malawi, Mozambique, Rwanda, Tanzania, Zaire, and Zambia).
Epidemic dysentery is a major problem among refugee populations, where overcrowding and poor sanitation facilitate transmission. Epidemics are characterized by severe disease, high death rates, person-to-person spread, and multiple antibiotic resistance. Worldwide, approximately 140 million people develop dysentery each year, and about 600,000 die. Most of these deaths occur in developing countries among children under age five. In the United States, only about 25,000 to 30,000 cases occur each year.
In sub-Saharan Africa, diarrheal diseases are a leading cause of death in children under age five. It is estimated that each child has five episodes of diarrhea per year and that 800,000 of those children will die from diarrhea and associated de-hydration.
Dysentery is most commonly caused by one of two different organisms: One is a bacterium called Shigella; the other is caused by an amoeba. Shigella is the most important cause of bloody diarrhea because it destroys cells that line the large intestine, which leads to mucosal ulcers in the intestine. The mucosal ulcers cause the bloody diarrhea. Ingesting as few as 10 to 100 bacteria, which can be contained in a tiny amount of infected food or water, can cause disease.
Amoebic dysentery is prevalent in regions where human excrement is used as fertilizer. The amoebas that cause dysentery can form cysts, which are like bacterial spores that can become inactive and highly resistant to environmental conditions. In other words, they can live a long time outside the body and then reactivate and cause disease when conditions become favorable.
Cysts and live amoebas are excreted in the feces of an infected person, but only the cysts can survive outside the body. The amoebic infection is milder in comparison with bacterial dysentery. Despite this, amoebic dysentery is more difficult to treat and cure; bacterial dysentery responds better and more quickly to treatment.
Both types of dysentery infect people of diverse age, sex, and ethnic backgrounds, although children are more susceptible.
The two primary causes of dysentery are the Shigella bacterium and an amoeba. Shigella can cause severe disease and epidemics, although it responds well to treatment. Dysentery caused by the amoeba is milder than its bacterial cousin, although it is quite difficult to treat and cure and often becomes chronic.
Patients with bacterial dysentery often have fever, abdominal cramps, rectal pain, and bloody stools. Occasionally, large portions of the intestinal membrane pass with particularly foul-smelling stool containing yellowish white mucus and/or blood. In nearly half the cases, Shigella does not cause bloody diarrhea.
When amoeba cysts are ingested with contaminated food or water, they germinate and develop into live amoebas in the intestine. The disease remains mild if the amoeba stay confined within the intestines. Like bacterial dysentery, invasion of the intestinal wall leads to fever, abdominal and rectal pain, and bloody diarrhea. Amoebic dysentery may occur in a chronic form when the amoebas invade blood vessels of the intestine and are carried to other parts of the body, causing amoebic abscesses of the liver and brain. About 40 percent of all untreated cases eventually cause nonintestinal infections, such as amoebic hepatitis.
The amoebic form of dysentery lives outside the body by forming cysts, which are similar to bacterial spores. Cysts have a tough outer wall that prevents different environmental conditions from killing the amoebas. Similar to a bear hibernating, the cysts are dormant until conditions are better—they invade a body that has the right temperature and nutrients—then they wake up and cause disease.
Dysentery is diagnosed from rectal swabs that show evidence of dysentery-causing Shigella bacteria or amoeba.
Disposing of Dysentery
Bacterial dysentery often subsides by itself, although treatment using antibiotics is recommended to prevent recurrence. Having drug-susceptibility tests performed before beginning treatment is important to determine which antibiotics will work best, because many organisms have become drug resistant. Shigella first began to acquire resistance in the 1940s and has become resistant to several classes of drugs since then.
Treating the dehydration that accompanies dysentery is also important. These symptoms should be treated with oral rehydration salts or, if severe, with intravenous fluids.
A combination of drugs is used to treat amoebic dysentery: an amoebicide to eradicate the organism from the intestinal tract, and an antibiotic to eliminate potential secondary bacterial infections.
Eradicating the Epidemic
Early detection and notification of epidemic dysentery, especially among adults, allows for speedy reaction to help fight the disease's spread. Hand-washing with soap and water can reduce secondary transmission of Shigella infections among household members. And among larger groups, such as within refugee camps, the most effective strategies to control transmission of epidemic Shigella are to …
Developing a Vaccine
There are no vaccines for dysentery, although there is a strong need, particularly because drug resistance often limits treatment options. There are currently several potential vaccines in the evaluation stages.
Contaminated water causes millions and millions of cases of disease every year. We have discussed cholera and dysentery in this section, but there are other diseases, too. Improved sanitation is key to controlling these diseases, but until conditions improve, it is important for victims to receive proper treatment and to be sure to prevent the severe dehydration that often occurs with diarrheal disease.
Excerpted from The Complete Idiot's Guide to Dangerous Diseases and Epidemics © 2002 by David Perlin, Ph.D., and Ann Cohen. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.