Dysentery

Definition

Dysentery is a general term for a group of gastrointestinal disorders characterized by inflammation of the intestines, particularly the colon. Characteristic features include abdominal pain and cramps, straining at stool (tenesmus), and frequent passage of watery diarrhea or stools containing blood and mucus. The English word dysentery comes from two Greek words meaning "ill" or "bad" and "intestine."

It should be noted that some doctors use the word "dysentery" to refer only to the first two major types of dysentery discussed below, while others use the term in a broader sense. For example, some doctors speak of schistosomiasis, a disease caused by a parasitic worm, as bilharzial dysentery, while others refer to acute diarrhea caused by viruses as viral dysentery.

Description

Dysentery is a common but potentially serious disorder of the digestive tract that occurs throughout the world. It can be caused by a number of infectious agents ranging from viruses and bacteria to protozoa and parasitic worms; it may also result from chemical irritation of the intestines. Dysentery is one of the oldest known gastrointestinal disorders, having been described as early as the Peloponnesian War in the fifth century b.c. Epidemics of dysentery were frequent occurrences aboard sailing vessels as well as in army camps, walled cities, and other places in the ancient world where large groups of human beings lived together in close quarters with poor sanitation. As late as the eighteenth and nineteenth centuries, sailors and soldiers were more likely to die from the "bloody flux" than from injuries received in battle. It was not until 1897 that a bacillus (rod-shaped bacterium) was identified as the cause of one major type of dysentery.

Dysentery in the modern world is most likely to affect people in the less developed countries and travelers who visit these areas. According to the Centers for Disease Control and Prevention (CDC), most cases of dysentery in the United States occur in immigrants from the developing countries and in persons who live in inner-city housing with poor sanitation. Other groups of people at increased risk of dysentery are military personnel stationed in developing countries, frequent travelers, children in day care centers, people in nursing homes, and men who have sex with other men.

Causes & symptoms

Causes

The most common types of dysentery and their causal agents are as follows:

• Bacillary dysentery. Bacillary dysentery, which is also known as shigellosis, is caused by four species of the genus Shigella: S. dysenteriae, the most virulent species and the one most likely to cause epidemics; S. sonnei, the mildest species and the most common form of Shigella found in the United States; S. boydii ; and S. flexneri. S. flexneri is the species that causes Reiter's syndrome, a type of arthritis that develops as a late complication of shigellosis. About 15,000 cases of shigellosis are reported to the CDC each year for the United States; however, the CDC maintains that the true number of annual cases may be as high as 450,000, since the disease is vastly underreported. About 85 percent of cases in the United States are caused by S. sonnei. The Shigella organisms cause the diarrhea and pain associated with dysentery by invading the tissues that line the colon and secreting an enterotoxin, or harmful protein that attacks the intestinal lining.
• Amebic dysentery. Amebic dysentery, which is also called intestinal amebiasis and amebic colitis, is caused by a protozoon, Entamoeba histolytica. E. histolytica, whose scientific name means "tissue-dissolving," is second only to the organism that causes malaria as a protozoal cause of death. E. histolytica usually enters the body during the cyst stage of its life cycle. The cysts may be found in food or water contaminated by human feces. Once in the digestive tract, the cysts break down, releasing an active form of the organism called a trophozoite. The trophozoites invade the tissues lining the intestine, where they are usually excreted in the patient's feces. They sometimes penetrate the lining itself, however, and enter the bloodstream. If that happens, the trophozoites may be carried to the liver, lung, or other organs. Involvement of the liver or other organs is sometimes called metastatic amebiasis.
• Balantidiasis, giardiasis, and cryptosporidiosis. These three intestinal infections are all caused by protozoa, Balantidium coli, Giardia lamblia, and Cryptosporidium parvum respectively. Although most people infected with these protozoa do not become severely ill, the disease agents may cause dysentery in children or immunocompromised individuals. There are about 3,500 cases of cryptosporidiosis reported to the CDC each year in the United States, and about 22,000 cases of giardiasis.

• Viral dysentery. Viral dysentery, which is sometimes called traveler's diarrhea or viral gastroenteritis, is caused by several families of viruses, including rotaviruses, caliciviruses, astroviruses, noroviruses, and adenoviruses. There are about 3.5 million cases of viral dysentery in infants in the United States each year, and about 23 million cases each year in adults. The CDC estimates that viruses are responsible for 9.2 million cases of dysentery related to food poisoning in the United States each year. Whereas most cases of viral dysentery in infants are caused by rotaviruses, caliciviruses are the most common disease agents in adults. Noroviruses were responsible for about half of the outbreaks of dysentery on cruise ships reported to the CDC in 2002.
• Dysentery caused by parasitic worms. Both whipworm (trichuriasis) and flatworm or fluke (schistosomiasis) infestations may produce the violent diarrhea and abdominal cramps associated with dysentery. Schistosomiasis is the second most widespread tropical disease after malaria. Although the disease is rare in the United States, travelers to countries where it is endemic may contract it. The World Health Organization (WHO) estimates that about 200 million people around the world carry the parasite in their bodies, with 20 million having severe disease.

Symptoms

In addition to the characteristic bloody and/or watery diarrhea and abdominal cramps of dysentery, the various types have somewhat different symptom profiles:

• Bacillary dysentery. The symptoms of shigellosis may range from the classical bloody diarrhea and tenesmus characteristic of dysentery to the passage of nonbloody diarrhea that resembles the loose stools caused by other intestinal disorders. The high fever associated with shigellosis begins within one to three days after exposure to the organism. The patient may also have pain in the rectum as well as abdominal cramping. The acute symptoms last for three to seven days, occasionally for as long as a month. Bacillary dysentery may lead to two potentially fatal complications outside the digestive tract: bacteremia (bacteria in the bloodstream), which is most likely to occur in malnourished children; and hemolytic uremic syndrome, a type of kidney failure that has a mortality rate above 50 percent.
• Amebic dysentery. Amebic dysentery often has a slow and gradual onset; most patients with amebiasis visit the doctor after several weeks of diarrhea and bloody stools. Fever is unusual with amebiasis unless the patient has developed a liver abscess as a complication of the infection. The most serious complication of amebic dysentery, however, is fulminant or necrotizing colitis, which is a severe inflammation of the colon characterized by dehydration, severe abdominal pain, and the risk of perforation (rupture) of the colon.
• Dysentery caused by other protozoa. Dysentery associated with giardiasis begins about 1-3 weeks after infection with the organism. It is characterized by bloating and foul-smelling flatus, nausea and vomiting, headaches, and low-grade fever. These acute symptoms usually last for three or four days. The symptoms of cryptosporidiosis are mild in most patients but are typically severe in patients with AIDS. Diarrhea usually starts between seven and 10 days after exposure to the organism and may be copious. The patient may have pain in the upper right abdomen, nausea, and vomiting, but fever is unusual.
• Viral dysentery. Viral dysentery has a relatively rapid onset; symptoms may begin within hours of infection. The patient may be severely dehydrated from the diarrhea but usually has only a low-grade fever. The diarrhea itself may be preceded by one to three days of nausea and vomiting. The patient's abdomen may be slightly tender but is not usually severely painful.
• Dysentery caused by parasitic worms. Patients with intestinal schistosomiasis typically have a gradual onset of symptoms. In addition to bloody diarrhea and abdominal pain, these patients usually have fatigue. An examination of the patient's colon will usually reveal areas of ulcerated tissue, which is the source of the bloody diarrhea.

Diagnosis

Patient history and physical examination

The physical examination in the primary care doctor's office will not usually allow the doctor to determine the specific parasite or other disease agent that is causing the bloody diarrhea and other symptoms of dysentery, although the presence or absence of fever may help to narrow the diagnostic possibilities. The patient's age and history are usually better sources of information. The doctor may ask about such matters as the household water supply and food preparation habits, recent contact with or employment in a nursing home or day care center, recent visits to tropical countries, and similar questions. The doctor will also need to know when the patient first noticed the symptoms.

The doctor will also evaluate the patient for signs of dehydration resulting from the loss of fluid through the intestines. Fatigue, drowsiness, dryness of the mucous membranes lining the mouth, low blood pressure, loss of normal skin tone, and rapid heartbeat (above 100 beats per minute) may indicate that the patient is dehydrated.

Laboratory tests

The most common laboratory test to determine the cause of dysentery is a stool sample. The patient should be asked to avoid using over-the-counter antacids or antidiarrheal medications until the sample has been collected, as these preparations can interfere with the test results. The organisms that cause cryptosporidiosis, bacillary dysentery, amebic dysentery, and giardiasis can be seen under the microscope, as can the eggs produced by parasitic worms. In some cases repeated stool samples, a sample of mucus from the intestinal lining obtained through a proctoscope, or a tissue sample from the patient's colon may be necessary to confirm the diagnosis. Antigen testing of a stool sample can be used to diagnose a rotavirus infection as well as parasitic worm infestations.

The doctor will also usually order a blood test to evaluate the electrolyte levels in the patient's blood in order to assess the need for rehydration.

Imaging studies

Imaging studies (usually CT scans, x rays, or ultrasound) may be performed in patients with amebic dysentery to determine whether the lungs or liver have been affected. They may also be used to diagnose schistosomiasis, as the eggs produced by the worms will show up on ultrasound or MRI studies of the liver, intestinal wall, or bladder.

Treatment

Medications are the primary form of treatment for dysentery:

• Bacillary dysentery. Dysentery caused by Shigella is usually treated with such antibiotics as trimethoprim-sulfamethoxazole (Bactrim, Septra), nalidixic acid (NegGram), or ciprofloxacin (Cipro, Ciloxan). Because the various species of Shigella are becoming resistant to these drugs, however, the doctor may prescribe one of the newer drugs described below. Patients with bacillary dysentery should not be given antidiarrheal medications, including loperamide (Imodium), paregoric, and diphenolate (Lomotil), because they may make the illness worse.
• Amebic dysentery. The most common drugs given for amebiasis are diloxanide furoate (Diloxide), iodoquinol (Diquinol, Yodoxin), and metronidazole (Flagyl). Metronidazole should not be given to pregnant women but paromomycin (Humatin) may be used instead. Patients with very severe symptoms may be given emetine dihydrochloride or dehydroemetine, but these drugs should be stopped once the patient's symptoms are controlled.
• Dysentery caused by other protozoa. Balantidiasis, giardiasis, and cryptosporidiosis are treated with the same drugs as amebic dysentery; patients with giardiasis resistant to treatment may be given albendazole (Zentel) or furazolidone (Furoxone).
• Viral dysentery. The primary concern in treating viral dysentery, particularly in small children, is to prevent dehydration. Antinausea and antidiarrhea medications should not be given to small children. Probiotics, including Lactobacillus casei and Saccharomyces boulardii, have been shown to reduce the duration and severity of viral diarrhea in small children by 30-70 percent.
• Dysentery caused by parasitic worms. Whipworm infestations are usually treated with anthelminthic medications, most commonly mebendazole (Vermox). Schistosomiasis may be treated with praziquantel (Biltricide), metrifonate (Trichlorfon), or oxamniquine, depending on the species causing the infestation.

Newer drugs that have been developed to treat dysentery include tinidazole (Tindamax, Fasigyn), an antiprotozoal drug approved by the Food and Drug Administration (FDA) in 2004 to treat giardiasis and amebiasis in adults and children over the age of three years. This drug should not be given to women in the first three months of pregnancy. In addition, adults taking tinidazole should not drink alcoholic beverages while using it, or for three days after the end of treatment. The other new drug is nitazoxanide (Alinia), another antiprotozoal medication that has the advantage of lacking the bitter taste of metronidazole and tinidazole.

Fluid replacement is given if the patient has shown signs of dehydration. The most common treatment is an oral rehydration fluid containing a precise amount of salt and a smaller amount of sugar to replace electrolytes as well as water lost through the intestines. Infalyte and Pedialyte are oral rehydration fluids formulated for the special replacement needs of infants and young children.

Surgery

Surgery is rarely necessary in treating dysentery, but may be required in cases of fulminant colitis, particularly if the patient's colon has perforated. Patients with liver abscesses resulting from amebic dysentery may also require emergency surgery if the abscess ruptures. In some cases exploratory surgery may be needed to determine whether severe abdominal pain is caused by schistosomiasis, amebic dysentery, or appendicitis.

Alternative treatments

There are a number of alternative treatments for dysentery, most of which are derived from plants used by healers for centuries. Because dysentery was known to ancient civilizations as well as modern societies, such alternative systems as traditional Chinese medicine (TCM) and Ayurvedic medicine developed treatments for it.

Ayurvedic medicine

Ayurvedic medicine recommends fruits and herbs, specifically cumin seed, bael fruit (Aegle marmelos, also known as Bengal quince), and arjuna (Terminalia arjuna ) bark for the treatment of dysentery. Ayurvedic practitioners may also give the patient dietary supplements known as Isabbael, Lashunadi Bati, and Bhuwaneshar Ras. To rehydrate the body, adult patients may be given a combination of slippery elm water and barley to drink, at least a pint per day.

Traditional Chinese medicine

To treat dysentery, traditional Chinese doctors use astringent drugs, which are intended to constrict or tighten mucous membranes and other body tissues to slow down fluid loss. Myrobalan fruit (Terminalia chebula ), nut galls (swellings produced on the leaves and stems of oak trees by the secretions of certain insects), and opium extracted from the opium poppy (Papaver somniferum ) are the natural materials most commonly used. Paregoric, a water-based solution of morphine that is still used in the West to treat diarrhea, is derived from the opium poppy.

Other plant-based remedies

Researchers in Mexico reported in early 2005 that the roots of Geranium mexicanum, a plant that produces a sap traditionally used to treat coughs or diarrhea, contains compounds that are active against both Giardia lamblia and Entamoeba histolytica. Plant biologists in Africa are studying the effectiveness of African mistletoe (Tapinanthus dodoneifolius ), a traditional remedy for dysentery among the Hausa and Fulani tribes of Nigeria.

Dietary supplements

A study published in the American Journal of Clinical Nutrition in early 2005 reported that supplemental zinc (twice the recommended daily dietary allowance) boosts the body's immune response during acute shigellosis.

Homeopathy

There are at least ten different homeopathic remedies used to treat diarrhea. Contemporary homeopaths, however, distinguish between diarrhea that can be safely treated at home with such homeopathic remedies as Podophyllum, Veratrum album, Bryonia, and Arsenicum, and diarrhea that indicates dysentery and should be referred to a physician. Signs of dehydration (loss of normal skin texture, dry mouth, sunken eyes), severe abdominal pain, blood in the stool, and unrelieved vomiting are all indications that mainstream medical care is required.

Prognosis

Most adults in developed countries recover completely from an episode of dysentery. Children are at greater risk of becoming dehydrated, however; bacillary dysentery in particular can lead to a child's death from dehydration in as little as 12-24 hours.

• Bacillary dysentery. Most patients recover completely from shigellosis, although their bowel habits may not become completely normal for several months. About 3 percent of people infected by S. flexneri will develop Reiter's syndrome, which may lead to a chronic form of arthritis that is difficult to treat. Elderly patients or those with weakened immune systems sometimes develop secondary bacterial infections after an episode of shigellosis.
• Amebic dysentery. Most people in North America who become infected with E. histolytica do not become severely ill. Patients who develop a severe case of amebic dysentery, however, are at increased risk for such complications as fulminant colitis or liver abscess. About 0.5 percent of patients with amebic dysentery develop fulminant colitis, but almost half of these patients die. Between 2 and 7 percent of cases of amebic liver abscess result in rupture of the abscess with a high mortality rate. Men are 7-12 times more likely to develop a liver abscess than women. Any patient diagnosed with amebic dysentery should have stool samples examined for relapse 1, 3, and 6 months after treatment with medications whether or not they have developed complications.
• Dysentery caused by other protozoa. Cryptosporidiosis may lead to respiratory infections or pancreatitis in patients with AIDS. The risk of these complications, however, is reduced in AIDS patients who are receiving highly active antiretroviral therapy (HAART).
• Viral dysentery. Most people in North America recover completely without complications unless they become severely dehydrated. Viral dysentery in children in developing countries, however, is a major cause of mortality.
• Dysentery caused by parasitic worms. Untreated whipworm infections can lead to loss of appetite, chronic diarrhea, and retarded growth in children. Untreated schistosomiasis can develop into a chronic intestinal disorder in which fibrous tissue, small growths, or strictures (abnormal narrowing) may form inside the intestine. Patients treated for schistosomiasis should have stool samples checked for the presence of worm eggs 3 and 6 months after the end of treatment.

Prevention

The disease agents that cause dysentery do not confer immunity against reinfection at a later date. As of 2005 there are no vaccines for bacillary dysentery or amebic dysentery; however, a vaccine against schistosomiasis is under investigation. An oral vaccine against rotavirus infections was developed for small children but was withdrawn in 2004 because it was associated with an increased risk of small-bowel disorders. Newer vaccines against rotaviruses and caliciviruses are being developed as of 2005.

Public health measures

Public health measures to control the spread of dysentery include the following:

• Requiring doctors to report cases of disease caused by Shigella, Entamoeba histolytica, and other parasites that cause dysentery. Careful reporting allows the CDC and state public health agencies to investigate local outbreaks and plan prevention efforts.
• Posting advisories for travelers about outbreaks of dysentery and other health risks in foreign countries. The Travelers' Health section of the CDC website (http://www.cdc.gov/travel/) is a good source of up-to-date information.
• Instructing restaurant workers and other food handlers about proper methods of hand washing, food storage, and food preparation.
• Instructing workers in day care centers and nursing homes about the proper methods for changing and cleaning soiled diapers or bedding.
• Inspecting wells, other sources of drinking water, and swimming pools for evidence of fecal contamination.

KEY TERMS

Anthelminthic (also spelled anthelmintic)— A type of drug or herbal preparation given to destroy parasitic worms or expel them from the body.

Bacillus— A rod-shaped bacterium. One common type of dysentery is known as bacillary dysentery because it is caused by a bacillus.

Enterotoxin— A type of harmful protein released by bacteria and other disease agents that affects the tissues lining the intestines.

Fulminant— Occurring or flaring up suddenly and with great severity. A potentially fatal complication of amebic dysentery is an inflammation of the colon known as fulminant colitis.

Probiotics— Food supplements containing live bacteria or other microbes intended to improve or restore the normal balance of microorganisms in the digestive tract.

Proctoscope— An instrument consisting of a thin tube with a light source, used to examine the inside of the rectum.

Protozoan (plural, protozoa)— A member of the simplest form of animal life, a one-celled organism. Amebic dysentery is caused by a protozoan.

Reiter's syndrome— A group of symptoms that includes arthritis, inflammation of the urethra, and conjunctivitis, and develops as a late complication of infection with Shigella flexneri. The syndrome was first described by a German doctor named Hans Reiter in 1918.

Tenesmus— Straining to urinate or defecate without being able to do so. Tenesmus is a characteristic feature of bacillary dysentery.

Trophozoite— The active feeding stage of a protozoal parasite, as distinct from its encysted stage.

Personal precautions

Individuals can lower their risk of contracting dysentery by the following measures:

• Not allowing anyone in the household who has been diagnosed with amebic or bacillary dysentery to prepare food or pour water for others until their doctor confirms that they are no longer carrying the disease agent.
• Avoiding anal sex or oral-genital contacts.
• Washing the hands carefully with soap and water after using the bathroom, and supervising the hand-washing of children in day care centers or those at home who are not completely toilet-trained.
• When traveling, drinking only boiled or treated water, and eating only cooked hot foods or fruits that can be peeled by the traveler.
• Avoiding swimming in fresh water in areas known to have outbreaks of schistosomiasis.

Resources

BOOKS

Cummings, Stephen, MD, and Dana Ullman, MPH. Everybody's Guide to Homeopathic Medicines, revised and expanded. New York: Jeremy P. Tarcher, 1991.

"Enterobacteriaceae Infections." Section 13, Chapter 161 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

"Intestinal Protozoa." Section 13, Chapter 161 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

Pelletier, Kenneth R., MD. The Best Alternative Medicine. New York: Simon & Schuster, 2002.

Reid, Daniel P. Chinese Herbal Medicine. Boston: Shambhala, 1993.

PERIODICALS

Calzada, F., J. A. Cervantes-Martinez, and L. Yepez-Mulia. "In vitro Antiprotozoal Activity from the Roots of Geranium mexicanum and Its Constituents on Entamoeba histolytica and Giardia lamblia." Journal of Ethnopharmacology 98 (April 8, 2005): 191-193.

Chijide, Valda M., MD, and Keith F. Woeltje, MD. "Balantidiasis." eMedicine, 12 March 2002. 〈http://www.emedicine.com/med/topic203.htm〉.

Deeni, Y. Y., and N. M. Sadiq. "Antimicrobial Properties and Phytochemical Constituents of the Leaves of African Mistletoe (Tapinanthus dodoneifolius (DC) Danser) (Loranthaceae): An Ethnomedicinal Plant of Hausalan, Northern Nigeria." Journal of Ethnopharmacology 83 (December 2002): 235-240.

Eisen, Damon, MD. "Cryptosporidiosis." eMedicine, 18 November 2004. 〈http://www.emedicine.com/med/topic484.htm〉.

Goodgame, Richard W., MD. "Gastroenteritis, Viral." eMedicine, 14 June 2004. 〈http://www.emedicine.com/MED/topic856.htm〉.

Hlavsa, M. C., J. C. Watson, and M. J. Beach. "Cryptosporidiosis Surveillance—United States 1999–2002." Morbidity and Mortality Weekly Report, Surveillance Summaries 54 (January 28, 2005): 1-8.

Hlavsa, M. C., J. C. Watson, and M. J. Beach. "Giardiasis Surveillance—United States, 1998–2002." Morbidity and Mortality Weekly Report, Surveillance Summaries 54 (January 28, 2005): 9-16.

Hu, F., R. Lu, B. Huang, and M. Liang. "Free Radical Scavenging Activity of Extracts Prepared from Fresh Leaves of Selected Chinese Medicinal Plants." Fitoterapia 75 (January 2004): 14-23.

Kroser, Joyann A., MD. "Shigellosis." eMedicine, 17 May 2002. 〈http://www.emedicine.com/med/topic2112.htm〉.

Nachimuthu, Senthil, MD, and Paul Piccione, MD. "Food Poisoning." eMedicine, 10 January 2005. 〈http://www.emedicine.com/med/topic807.htm〉.

Pennardt, Andre, MD. "Giardiasis." eMedicine, 25 June 2004. 〈http://www.emedicine.com/emerg/topic215.htm〉.

Rahman, M. J., P. Sarker, S. K. Roy, et al. "Effects of Zinc Supplementation as Adjunct Therapy on the Systemic Immune Responses in Shigellosis." American Journal of Clinical Nutrition 81 (February 2005): 495-502.

Scoggins, Thomas, MD, and Igor Boyarsky, DO. "Reiter Syndrome." eMedicine, 7 December 2004. 〈http://www.emedicine.com/EMERG/topic498.htm〉.

Swords, Robert, MD, and J. Robert Cantey, MD. "Amebiasis." eMedicine, 22 February 2002. 〈http://www.emedicine.com/med/topic116.htm〉.

White, C. A. Jr. "Nitazoxanide: A New Broad-Spectrum Antiparasitic Agent." Expert Review of Anti-Infective Therapy 2 (February 2004): 43-49.

Wingate, D., S. F. Phillips, S. J. Lewis, et al. "Guidelines for Adults on Self-Medication for the Treatment of Acute Diarrhea." Alimentary Pharmacology and Therapeutics 15 (June 2001): 773-782.

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. 〈http://www.cdc.gov〉

Infectious Diseases Society of America (IDSA). 66 Canal Center Plaza, Suite 600, Alexandria, VA 22314. (703) 299-0200. Fax: (703) 299-0204. 〈http://www.idsociety.org〉.

World Health Organization (WHO). 〈http://www.who.int/en/〉.

OTHER

Centers for Disease Control and Prevention. Disease Information. "Shigellosis." 〈http://www.cdc.gov/ncidod/dbmd/diseaseinfo/shigellosis_t.htm〉

Centers for Disease Control and Prevention, Division of Parasitic Diseases. Fact Sheet. "Amebiasis." 〈http://www.cdc.gov/ncidod/dpd/parasites/amebiasis/factsht_amebiasis.htm〉

Centers for Disease Control and Prevention, National Center for Infectious Diseases, Travelers' Health. "New Medication Approved for Treatment of Giardiasis and Amebiasis." 〈http://www.cdc.gov/travel/other/tinidazole_approval_2004.htm〉

World Health Organization. "Shigella." 〈http://www.who.int/topics/shigella/en/〉.

Dysentery

Introduction

Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues

Primary source connection

BIBLIOGRAPHY

Introduction

Dysentery is the name given to an inflammation of the intestines, and especially the colon, that leads to abdominal pain and frequent stools which contain blood and mucus. Dysentery can be caused by bacteria, protozoa, worms, or even non-infectious agents. Shigella species are the causative agent in most cases of bacterial dysentery. Entamoeba histolytica, a protozoa, is the main cause of amebic dysentery.

Overcrowding and poor hygiene are major risk factors for dysentery. It occurs all around the world, among people of all ages. Dysentery is sometimes known as “travelers’ diarrhea” because it often affects those who visit developing countries. Although the disease normally clears up without treatment, antibiotics and drugs to get rid of amebic parasites might be necessary. Prior to the advent of antibiotics and improved sanitation, dysentery could be fatal and indeed, claimed the lives of many famous figures, including King Henry V of England (1387–1422) and the Spanish explorer Hernando Cortes (1485–1547).

Disease History, Characteristics, and Transmission

The four main Shigella species responsible for bacterial dysentery are S. sonnei, S. flexneri, S.boydii and S. dysenteriae and this disease is sometimes known as shigellosis. The Shigellae are rod-shaped bacteria of one to two millimeters in diameter, Gram-negative, and closely related to the Escherichia genus. Infection with Shigella is sometimes known as shigellosis. Gram-negative refers to the way bacteria interact with the Gram stain when being prepared for microscopic examination. Meanwhile, amebic dysentery—also called amebiasis—is caused by a single-celled protozoan parasite called Entamoeba histolytica.

The incubation period of shigellosis is usually one to three days. For amebic dysentery, the incubation time is much longer—maybe up to one year. Therefore, returning travelers who have acquired amebic dysentery abroadmay not immediately make the connection between infection and symptoms, which may delay diagnosis.

WORDS TO KNOW

GRAM-NEGATIVE: A method of identifying bacteria based on whether crystal-violet dye is retained or not retained after being stained and decolorized with alcohol in a process called Gram's method.

INCUBATION PERIOD: Incubation period refers to the time between exposure to disease causing virus or bacteria and the appearance of symptoms of the infection. Depending on the microorganism, the incubation time can range from a few hours (an example is food poisoning due to Salmonella) to a decade or more (an example is acquired immunodeficiency syndrome, or AIDS).

MORTALITY: Mortality is the condition of being susceptible to death. The term “mortality” comes from the Latin word mors, which means “death.” Mortality can also refer to the rate of deaths caused by an illness or injury, i.e., “Rabies has a high mortality.”

PROTOZOA: Single-celled animal-like microscopic organisms that live by taking in food rather than making it by photosynthesis and must live in the presence of water. (Singular: protozoan.) Protozoa are a diverse group of single-celled organisms, with more than 50,000 different types represented. The vast majority are microscopic, many measuring less than 5 one-thousandth of an inch (0.005 millimeters) but some, such as the freshwater Spirostomun, may reach 0.17 inches (3 millimeters) in length, large enough to enable it to be seen with the naked eye.

RELAPSE: Relapse is a return of symptoms after the patient has apparently recovered from a disease.

SENTINEL: Sentinel surveillance is a method in epidemiology where a subset of the population is surveyed for the presence of communicable diseases. Also, a sentinel is an animal used to indicate the presence of disease within an area.

SEPSIS: Sepsis refers to a bacterial infection in the bloodstream or body tissues. This is a very broad term covering the presence of many types of microscopic disease-causing organisms. Sepsis is also called bacteremia. Closely related terms include septicemia and septic syndrome. According to the Society of Critical Care Medicine, severe sepsis affects about 750,000 people in the United States each year. However, it is predicted to rapidly rise to one million people by 2010 due to the aging U.S. population. Over the decade of the 1990s, the incident rate of sepsis increased over 91%.

The symptoms of shigellosis and amebic dysentery are similar, the chief one being diarrhea containing blood and mucus. Amebic dysentery is more likely to produce blood. There may also be severe pain in the abdomen, fever, nausea and vomiting. Shigellosis tends to produce a watery diarrhea that progresses to dysentery, especially when S. dysenteriae and S. flexneri are involved.

Symptoms of dysentery, including the frequency of attacks of diarrhea, can range from mild to severe. Complications are more likely with S. dysenteriae and include sepsis (blood poisoning) and kidney failure. Blood clots may also be seen in the liver and the spleen. Dysentery with severe complications can have a mortality (death) rate of 5–20%. However, the symptoms of most cases of dysentery last for only a few days, although relapse and chronic infection can also occur.

The fecal-oral route is important in the transmission of Shigella—that is, eating or drinking contaminated food or water. Cases in Europe have been linked to infected milk and food. Houseflies also carry the disease. Dysentery is highly infectious and can also be transmitted just by contact with infected individuals. Shigella species enter through the mouth and progress to the colon where they multiply producing the severe inflammation which causes the symptoms of the disease. A person with shigellosis may remain infectious for up to four weeks after the onset of symptoms.

Amebic dysentery is transmitted in a similar way. In part of its life cycle, the amebae can exist as a cyst—a group of cells surrounded by a wall that can survive the acid of the stomach and progress to the intestines. The cysts can stick to the walls of the colon, causing bleeding ulcers, loss of appetite, and weight loss. The cysts are passed in the feces and can infect others under conditions of poor sanitation.

Scope and Distribution

Dysentery has long had an impact on human health, but it was not until the nineteenth century that the cause was realized to be either bacterial or amoebic. The Shigella get their name from Kiyoshi Shiga (1871– 1951) who discovered them in 1898. Dysentery has caused massive casualties in conflicts ranging from the Peloponnesian War in 431 BC to World War II (1939– 1945). In the American Civil War (1861–1865), there were nearly two million cases of diarrhea, most of which was probably dysentery, resulting in over 44,000 deaths. It has only been with the advent of antibiotics that dysentery has ceased to be such a major problem in military campaigns.

S. dysenteri causes most outbreaks of dysentery in developing countries, in the tropics and subtropics and under conditions of overcrowding or war. Epidemic dysentery in the tropics is more common in the rainy season, perhaps because people tend to spend more time indoors together and sanitation suffers from the abundance of surface water. S. sonnei and S. flexneri are the most common causes of shigellosis in the United States, England, Europe, Egypt, the Middle East, and Asia. S. boydii is found mainly in India and Egypt, although strains of all four species have been found in the U.S. as well.

Shigellosis is endemic throughout the world, but is more common in less developed countries. In Europe, the United States, and other developed regions, shigellosis tends to be a disease of institutions—nursery schools, mental institutions, prisons, and military barracks. In the U.S. and the United Kingdom, shigellosis is a notifiable disease.

Around 10% of the world's population is infected with Entamoeba histolytica, but fewer than 10% of those infected exhibit any signs of disease. Infection is prevalent in Central and South America, southern and western Africa, the Southeast Asia, India, and China. Amebic dysentery is relatively rare in Australia, New Zealand, Canada, the United States and Europe. However, travelers may become infected abroad. Pregnant women, children, and people in developing nations are most at risk to contract amebic dysentery.

IN CONTEXT: DISEASE IN DEVELOPING NATIONS

Acute hunger can cause people to die of starvation directly, but there are many more individuals who may survive famine, only to be faced with the health problems that often accompany undernourishment and vitamin and mineral deficiencies. Common effects of malnutrition include stunted growth, weakness, and susceptibility to disease. People who are malnourished often have poor concentration, which exacerbates the problem of hunger, as it is difficult for hungry people to work in fields, or earn money for buying food. Pregnant women, those who are breast-feeding newborns, and children are the most vulnerable to hunger related problems. Over 150 million children, worldwide, below the age of five, are said to be underweight. Eleven million children under the age of five die each year, with over half the deaths directly related to malnutrition. Typically these children do not die from starvation itself, but rather from the diseases that strike a weak and vulnerable body, whose immune system is likely unable to put up a defense. The four most common childhood illnesses in developing countries are diarrhea, respiratory illness, malaria, and measles.

Treatment and Prevention

Most cases of bacterial and amebic dysentery resolve with rest and drinking plenty of fluids to replace that which is lost from the diarrhea. This is especially important for babies with dysentery as they can become rapidly dehydrated. Sometimes antibiotic treatment, including hospitalization for intravenous therapy is needed. Trimethoprim-sulfamethoxazole or ampicillin are often used.

A good standard of personal hygiene will prevent the transmission of dysentery. This means frequent handwashing, especially after using the toilet or after contact with someone who is infected with Shigella. Hands should also be washed before handling and cooking food, eating, handling babies, and feeding the young or elderly. To avoid spreading infection, personal items like towels or face cloths should not be shared.

Travelers should avoid drinking tap water in countries known to have poor sanitation. Ice cubes, salad, and uncooked vegetables should also be avoided, because these could have been washed in contaminated water. A child who has had dysentery should stay away from school or nursery care for at least 48 hours after symptoms have ceased. An adult with dysentery should not return to work in a food or healthcare environment without first consulting their employer.

Impacts and Issues

There are approximately 165 million cases of shigellosis worldwide each year. Shigellosis disproportionately affects developing nations. The United Nations World Health Organization (WHO) reports 163.2 million annual cases in developing countries, compared to 1.5 million cases in industrialized countries.

Among residents of industrialized nations, the increased popularity of international travel accounts for a significant percentage of dysentery cases. The WHO estimates that there are approximately 580,000 reported cases of tourism-related shigellosis annually. The Centers for Disease Control (CDC) and several international health organizations publish infectious disease warnings and vaccination and medication advisories for travelers. Many travelers’ warnings also contain information on the quality and safety of local water. Individuals should consult these publications before traveling and follow their recommendations.

Dysentery is common wherever sanitation is inadequate or lacking, as with so many other water-borne infections. Therefore, development of adequate sewage disposal and access to clean drinking water should be a priority in helping prevent this globally important disease.

The WHO estimates that over one billion people worldwide do not have daily access to clean water. A greater number of people live in areas that lack basic sanitation systems. In 2005, the United Nations announced an initiative to halve by 2015 the number of people worldwide who lack potable water. The International Decade for Action, “Water for Life” project involves several U.N. and government agencies, as well as private charitable and health organizations.

Primary source connection

In this online news article, author Heidi Ledford discusses how travelers returning home inadvertently served as sentinels (lookouts) for an outbreak of Shigella in Africa in the 1990s, and how similar cases could alert health authorities in developing countries to future outbreaks if networks for sharing data are improved. Ledford has a PhD in plant biology and is a science journalist based in Boston, Massachusetts.

See AlsoAmebiasis; Shigellosis; War and Infectious Disease.

BIBLIOGRAPHY

Books

Ericsson, Charles D. Traveler's Diarrhea Hamilton, ON, Canada: BC Decker, 2003.

Web Sites

Centers for Disease Control and Prevention (CDC). “Amebiasis.” Jan 21, 2004 <http://www.cdc.gov/ncidod/dpd/parasites/amebiasis/factsht_amebiasis.htm> (accessed May 12, 2007).

Tropical Medicine Central Resource. “Shigellosis.” <http://tmcr.usuhs.mil/tmcr/chapter19/intro.htm> (accessed).

Susan Aldridge

Dysentery

Shigellosis

Amebic dysentery

Dysentery, which was historically called bloody flux or flux, is an infectious disease that involves severe diarrhea along with blood within the feces. The illness has ravaged armies and prisoner-of-war camps throughout history. The disease still is a major problem in tropical countries with primitive sanitary facilities. Refugee camps in Africa resulting from many civil wars are major sinks of infestation for dysentery.

Shigellosis

The acute form of dysentery, called shigellosis or bacillary dysentery, is caused by the bacillus (bacterium) of the genus Shigella, which is divided into four subgroups and distributed worldwide. Type A, Shigella dysenteriae, is a particularly virulent species. Infection begins from the solid waste from someone infected with the bacterium. Contaminated soil or water that gets on the hands of an individual often is conveyed to the mouth, where the person contracts the infection. Flies help to spread the bacillus.

Young children living in primitive conditions of overcrowded populations are especially vulnerable to the disease. Adults, though susceptible, usually will have less severe disease because they have gained a limited resistance. Immunity as such is not gained by infection, however, since an infected person can become re-infected by the same species of Shigella.

Once the bacterium has gained entrance through the mouth it travels to the lower intestine (colon) where it penetrates the mucosa (lining) of the intestine. In severe cases the entire colon may be involved, but usually only the lower half of the colon is involved. The incubation period is one to four days, that is the time from infection until symptoms appear.

Symptoms may be sudden and severe in children. They experience abdominal pain or distension, fever, loss of appetite, nausea, vomiting, and diarrhea. Blood and pus will appear in the stool, and the child may pass 20 or more bowel movements a day. Left untreated, he/she will become dehydrated from loss of water and will lose weight rapidly. Death can occur within 12 days of infection. If treated or if the infection is weathered, the symptoms will disappear within approximately two weeks.

Adults experience a less severe course of disease. They will initially feel a griping pain in the abdomen, develop diarrhea, though without any blood in the stool at first. Blood and pus will appear soon, however, as episodes of diarrhea recur with increasing frequency. Dysentery usually ends in the adult within four to eight days in mild cases and up to six weeks in severe infections.

Shigella dysenteriae brings about a particularly virulent infection that can be fatal within 12 to 24 hours. The patient has little or no diarrhea, but experiences delirium, convulsions, and lapses into a coma. Fortunately infection with this species is uncommon.

Treatment of the patient with dysentery usually is by fluid therapy to replace the liquid and electrolytes lost in sweating and diarrhea. Antibiotics may be used, but some Shigella species have developed resistance to them, so they may be relatively ineffective. Fluid therapy should be tendered with great care because patients often are very thirsty and will overindulge in fluids if given access to them. A hot water bottle may help to relieve abdominal cramps.

Some individuals can harbor the bacterium without having symptoms. Like those who are convalescent from the disease, the carriers without symptoms can spread the disease. This action may occur by someone with improperly washed hands preparing food, which becomes infected with the organism.

Amebic dysentery

Another form of dysentery called amebic dysentery or intestinal amebiasis is spread by a protozoan, Entamoeba histolytica. The protozoan occurs in an active form, that which infects the bowel, and an encysted form, that which forms the source of infection. If the patient develops diarrhea the active form of amoeba will pass from the bowel and rapidly die. If no diarrhea is present the amoeba will form a hard cyst about itself and pass from the bowel to be picked up by another victim. Once ingested it will lose its shell and begin the infectious cycle. Amebic dysentery can be waterborne, so anyone drinking infested water that is not purified is susceptible to infection.

Amebic dysentery is common in the tropics and relatively rare in temperate climates. Infection may be so subtle as to be practically unnoticed. Intermittent bouts of diarrhea, abdominal pain, flatulence, and cramping mark the onset of infection. Spread of infection may occur with the organisms entering the liver, so abdominal tenderness may occur over the area of the liver. Because the amoeba invades the lining of the colon, some bleeding may occur, and in severe infections the patient may require blood transfusions to replace that which is lost.

Treatment again is aimed at replacement of lost fluids and the relief of symptoms. Microscopic examination of the stool will reveal the active protozoan or its cysts. Special medications aimed at eradicating the infectious organism may be needed.

An outbreak of amebic dysentery can occur seemingly mysteriously because the carrier of the amoeba may be without symptoms, especially in a temperate zone. This can be a person with inadequate sanitation who can spread the disease through food that he/she has handled. Often the health officials can trace a disease outbreak back to a single kitchen and then test the cooks for evidence of amebic dysentery.

Before the idea of the spread of infectious agents was understood, dysentery often was responsible for more casualties among the ranks of armies than was actual combat. It also was a constant presence among prisoners who often died because little or no medical assistance was available to them. It is still a condition present throughout the world that requires vigilance. Prevention is the most effective means to maintain the health of populations living in close quarters. Hand washing, especially among food preparation personnel, and water purification are the most effective means of prevention. Adequate latrine facilities also help to contain any infectious human waste. A carefully administered packet of water and electrolytes to replace those lost can see a child through the infection.

See also Digestive system.

Larry Blaser

Dysentery

Dysentery is an infectious disease that has ravaged armies and prisoner-of-war camps throughout history. The disease still is a major problem in tropical countries with primitive sanitary facilities. Refugee camps in Africa resulting from many civil wars are major sinks of infestation for dysentery.

Shigellosis

The acute form of dysentery, called shigellosis or bacillary dysentery, is caused by the bacillus (bacterium) of the genus Shigella, which is divided into four subgroups and distributed worldwide. Type A, Shigella dysenteriae, is a particularly virulent species . Infection begins from the solid waste from someone infected with the bacterium. Contaminated soil or water that gets on the hands of an individual often is conveyed to the mouth, where the person contracts the infection. Flies help to spread the bacillus.

Young children living in primitive conditions of overcrowded populations are especially vulnerable to the disease. Adults, though susceptible, usually will have less severe disease because they have gained a limited resistance. Immunity as such is not gained by infection, however, since an infected person can become reinfected by the same species of Shigella.

Once the bacterium has gained entrance through the mouth it travels to the lower intestine (colon) where it penetrates the mucosa (lining) of the intestine. In severe cases the entire colon may be involved, but usually only the lower half of the colon is involved. The incubation period is one to four days, that is the time from infection until symptoms appear.

Symptoms may be sudden and severe in children. They experience abdominal pain or distension, fever, loss of appetite, nausea, vomiting, and diarrhea. Blood and pus will appear in the stool, and the child may pass 20 or more bowel movements a day. Left untreated, he will become dehydrated from loss of water and will lose weight rapidly. Death can occur within 12 days of infection. If treated or if the infection is weathered, the symptoms will disappear within approximately two weeks.

Adults experience a less severe course of disease. They will initially feel a griping pain in the abdomen, develop diarrhea, though without any blood in the stool at first. Blood and pus will appear soon, however, as episodes of diarrhea recur with increasing frequency. Dysentery usually ends in the adult within four to eight days in mild cases and up to six weeks in severe infections.

Shigella dysenteriae brings about a particularly virulent infection that can be fatal within 12-24 hours. The patient has little or no diarrhea, but experiences delirium, convulsions, and lapses into a coma . Fortunately infection with this species is uncommon.

Treatment of the patient with dysentery usually is by fluid therapy to replace the liquid and electrolytes lost in sweating and diarrhea. Antibiotics may be used, but some Shigella species have developed resistance to them, so they may be relatively ineffective. Fluid therapy should be tendered with great care because patients often are very thirsty and will overindulge in fluids if given access to them. A hot water bottle may help to relieve abdominal cramps.

Some individuals can harbor the bacterium without having symptoms. Like those who are convalescent from the disease, the carriers without symptoms can spread the disease. This may occur by someone with improperly washed hands preparing food, which becomes infected with the organism .

Amebic dysentery

Another form of dysentery called amebic dysentery or intestinal amebiasis is spread by a protozoan, Entamoeba histolytica. The protozoan occurs in an active form, that which infects the bowel, and an encysted form, that which forms the source of infection. If the patient develops diarrhea the active form of amoeba will pass from the bowel and rapidly die. If no diarrhea is present the amoeba will form a hard cyst about itself and pass from the bowel to be picked up by another victim. Once ingested it will lose its shell and begin the infectious cycle. Amebic dysentery can be waterborne, so anyone drinking infested water that is not purified is susceptible to infection.

Amebic dysentery is common in the tropics and relatively rare in temperate climates. Infection may be so subtle as to be practically unnoticed. Intermittent bouts of diarrhea, abdominal pain, flatulence, and cramping mark the onset of infection. Spread of infection may occur with the organisms entering the liver, so abdominal tenderness may occur over the area of the liver. Because the amoeba invades the lining of the colon, some bleeding may occur, and in severe infections the patient may require blood transfusions to replace that which is lost.

Treatment again is aimed at replacement of lost fluids and the relief of symptoms. Microscopic examination of the stool will reveal the active protozoan or its cysts. Special medications aimed at eradicating the infectious organism may be needed.

An outbreak of amebic dysentery can occur seemingly mysteriously because the carrier of the amoeba may be without symptoms, especially in a temperate zone. This is the person with inadequate sanitation who can spread the disease through food that he has handled. Often the health officials can trace a disease outbreak back to a single kitchen and then test the cooks for evidence of amebic dysentery.

Before the idea of the spread of infectious agents was understood, dysentery often was responsible for more casualties among the ranks of armies than was actual combat. It also was a constant presence among prisoners who often died because little or no medical assistance was available to them. It is still a condition present throughout the world that requires vigilance. Prevention is the most effective means to maintain the health of populations living in close quarters. Hand washing, especially among food preparation personnel, and water purification are the most effective means of prevention. Adequate latrine facilities also help to contain any infectious human waste. A carefully administered packet of water and electrolytes to replace those lost can see a child through the infection.

See also Digestive system.

Larry Blaser

Dysentery

Dysentery is an infectious disease that has ravaged armies, refugee camps, and prisoner-of-war camps throughout history. The disease still is a major problem in developing countries with primitive sanitary facilities.

The acute form of dysentery, called shigellosis or bacillary dysentery, is caused by the bacillus (bacterium) of the genus Shigella, which is divided into four subgroups and distributed worldwide. Type A, Shigella dysenteriae, is a particularly virulent species. Infection begins from the solid waste from someone infected with the bacterium. Contaminated soil or water that gets on the hands of an individual often is conveyed to the mouth, where the person contracts the infection. Flies help to spread the bacillus.

Young children living in primitive conditions of overcrowded populations are especially vulnerable to the disease. Adults, though susceptible, usually will have less severe disease because they have gained a limited resistance. Immunity as such is not gained by infection, however, and an infected person can become reinfected by the same species of Shigella .

Once the bacterium has gained entrance through the mouth, it travels to the lower intestine (colon) where it penetrates the mucosa (lining) of the intestine. In severe cases, the entire colon may be involved, but usually only the lower half of the colon is involved. The incubation period is one to four days, that is the time from infection until symptoms appear.

Symptoms may be sudden and severe in children. They experience abdominal pain or distension, fever, loss of appetite, nausea, vomiting, and diarrhea. Blood and pus will appear in the stool, and the child may pass 20 or more bowel movements a day. Left untreated, he will become dehydrated from loss of water and will lose weight rapidly. If untreated, death may occur within 12 days of infection. If treated or if the infection is weathered, the symptoms will subside within approximately two weeks.

Adults experience a less severe course of disease. They will initially feel a griping pain in the abdomen, develop diarrhea, though without any blood in the stool at first. Blood and pus will appear soon, however, as episodes of diarrhea recur with increasing frequency. Dysentery usually ends in the adult within four to eight days in mild cases, and up to six weeks in severe infections.

Shigella dysenteriae brings about a particularly virulent infection that can be fatal within 12 to 24 hours. The patient has little or no diarrhea, but experiences delirium, convulsions, and lapses into a coma. Fortunately, infection with this species is uncommon.

Treatment of the patient with dysentery usually is by fluid therapy to replace the liquid and electrolytes lost in sweating and diarrhea. Antibiotics may be used, but some Shigella species have developed resistance to them, and in these cases, antibiotics may be relatively ineffective.

Some individuals harbor the bacterium without having symptoms. Like those who are convalescent from the disease, the carriers without symptoms can spread the disease. This may occur by someone with improperly washed hands preparing food, which becomes infected with the organism.

Another form of dysentery called amebic dysentery or intestinal amebiasis is spread by a protozoan, Entamoeba histolytica. The protozoan occurs in an active form, which infects the bowel, and an encysted form, which forms the source of infection. If the patient develops diarrhea, the active form of amoeba will pass from the bowel and rapidly die. If no diarrhea is present, the amoeba will form a hard cyst about itself and pass from the bowel to be picked up by another victim. Once ingested, it will lose its shell and begin the infectious cycle. Amebic dysentery can be waterborne, so anyone drinking infested water that is not purified is susceptible to infection.

Amebic dysentery is common in the tropics and relatively rare in temperate climates. Infection may be so subtle as to be practically unnoticed. Intermittent bouts of diarrhea, abdominal pain, flatulence, and cramping mark the onset of infection. Spread of infection may occur with the organisms entering the liver, so abdominal tenderness may occur over the area of the liver. Because the amoeba invades the lining of the colon, some bleeding may occur, and in severe infections, the patient may require blood transfusions to replace lost blood.

Treatment, again, is aimed at replacement of lost fluids and the relief of symptoms. Microscopic examination of the stool will reveal the active protozoan or its cysts. Special medications aimed at eradicating the infectious organism may be needed.

An outbreak of amebic dysentery can occur seemingly mysteriously because the carrier of the amoeba may be without symptoms, especially in a temperate zone. A person with inadequate sanitation can spread the disease through food that he has handled. Often, health officials can trace a disease outbreak back to a single kitchen and then test the cooks for evidence of amebic dysentery.

Before the idea of the spread of infectious agents was understood, dysentery often was responsible for more casualties among the ranks of armies than was actual combat. It also was a constant presence among prisoners, who often died because little or no medical assistance was available to them. Dysentery remains a condition present throughout the world that requires vigilance. Prevention is the most effective means to maintain the health of populations living in close quarters. Hand washing, especially among food preparation personnel, and water purification are the most effective means of prevention.

See also Waste water treatment; Water pollution and purification; Water quality