Medical Conditions - Dysentery

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The Facts

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. It usually lasts for 3 to 7 days.

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.


Dysentery can have a number of causes. Bacterial infections are by far the most common causes of dysentery. These infections include Shigella, Campylobacter, E. coli, and Salmonella species of bacteria. The frequency of each pathogen varies considerably in different regions of the world. Dysentery is rarely caused by chemical irritants or by intestinal worms.

The Shigella and Campylobacter bacteria that cause bacillary dysentery are found all over the world. They penetrate the lining of the intestine, causing swelling, ulcerations, and severe diarrhea containing blood and pus. Both infections are spread by ingestion of food or water contaminated with infected feces. 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. Young children (ages 1 to 5) living in poverty are most likely to contract shigellosis, campylobacteriosis, or salmonellosis. 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.

Intestinal amoebiasis is caused by a protozoan parasite, Entamoeba histolytica. The amoeba can exist for long periods of time in the large bowel (colon). In the vast majority of cases, amoebiasis causes no symptoms – only 10% of infected individuals become ill. It is uncommon except in developing countries in the world’s tropical zones, where it is very prevalent. People can become infected after ingesting water or food contaminated with somebody’s excreted parasites.  People are at high risk of acquiring the parasite through food and water if the water for household use isn’t separated from waste water. The parasites can also enter through the mouth when hands are washed in contaminated water. If people neglect to wash properly before preparing food, the food may become contaminated. Fruits and vegetables can be contaminated if washed in polluted water or grown in soil fertilized by human waste.

Having sex that involves anal contact may spread amoebic and bacillary dysentery. This is especially true if the sex included direct anal-oral contact, or oral contact with an object (e.g., fingers) that touched or was in the anus of an infected person.

Symptoms and Complications

The main symptom of dysentery is frequent near-liquid diarrhea flecked with blood, mucus, or pus. Other symptoms include:

  • sudden onset of high fever (at least 100.4°F or 38°C) and chills
  • abdominal pain
  • cramps and bloating
  • flatulence (passing gas)
  • urgency to pass stool
  • feeling of incomplete emptying
  • loss of appetite
  • weight loss
  • headache
  • fatigue
  • nausea
  • vomiting
  • dehydration

Other symptoms may be intermittent and may include recurring low fevers, abdominal cramps, increased gas, and milder and firmer diarrhea. You may feel weak and tired, or lose weight over a prolonged period (emaciation). Mild cases of bacillary dysentery may last 4 to 8 days, while severe cases may last 3 to 6 weeks. Amoebiasis starts more gradually and usually lasts about 2 weeks.

Bacillary dysentery symptoms begin within 2 to 10 days of infection. In children, the illness starts with fever, nausea, vomiting, abdominal cramps, and diarrhea. Episodes of diarrhea may increase to as much as once an hour with blood, mucus, and pus in the child’s stool. Vomiting and diarrhea may result in rapid and severe dehydration, which may lead to shock and death if not treated. Signs of dehydration include an extremely dry mouth, sunken eyes, and poor skin tone. Children and infants will be thirsty, restless, irritable, and possibly lethargic. Children may not be able to produce tears or urine, the latter appearing very dark and concentrated.

Complications from bacillary dysentery include delirium, convulsions, and coma. A very severe infection like this can be fatal within 24 hours. However, the vast majority of infections are self-limited and resolve spontaneously without treatment.

People with amoebic dysentery may experience other problems associated with amoebiasis. The most frequent complication results when parasites spread to the liver, causing an amoebic abscess. In this case, you would have a high fever and experience weight loss and right shoulder or upper abdominal pain. If the infection of the bowel is especially virulent, the intestinal ulcerations may lead to bowel perforation and death. The parasites may rarely spread through the bloodstream, causing infection in the lungs, brain, and other organs.

Making the Diagnosis

If a doctor suspects dysentery, a stool sample usually will be required for analysis. For bacterial infections such as shigella, the diagnosis is made by culture of the stool. Unfortunately, such cultures are not available in most developing countries and the diagnosis is made clinically on the basis of symptoms. Amoebiasis is often diagnosed by finding parasites under a microscope. An antibody blood test helps to confirm the diagnosis of amoebic dysentery or liver abscess.

The E. histolytica has an identical "twin brother," Entamoeba dispar, a harmless amoeba that looks identical to E. histolytica under the microscope. It never produces symptoms and does not require treatment. In developing countries, the distinction is not usually made – individuals found to have amoebae in their stools are treated whether or not it is clear that the infection is causing symptoms. Of those diagnosed with amoebae in their stools, 90% have the harmless E. dispar.

Treatment and Prevention

Antiparasitic medications such as metronidazole*, paromomycin and iodoquinol, are commonly used to treat dysentery caused by amoebiasis. Sometimes antibiotics like ciprofloxacin, ofloxacin, levofloxacin, or azithromycin are used to treat the organisms causing bacillary dysentery. People who still have diarrhea symptoms after 2 days of treatment should consult with their doctor, as you may need to try something else. If you travel, you should carry a one- to three-day self-treatment antibiotic regimen such as ciprofloxacin and use it in the case of sudden moderate-to-severe diarrheal illness. Bismuth subsalicylate (Pepto-Bismol®) taken preventatively can also be helpful for some travellers. In addition, use the antidiarrheal medication loperamide to slow the bowel and prevent dehydration. It is important to use antidiarrheal medications only until you can seek medical attention or to help you return home following a vacation. If you have dysentery caused by bacteria or parasite, you will want your body to expel the "bug." Consult your doctor if your child under 2 years of age has dysentery.

It is most important to replace the fluids lost from diarrhea. In mild cases, soft drinks, juices, and bottled water will be enough. More severe diarrhea should be treated with solutions that contain electrolytes such as potassium, salt, and sucrose. For severe diarrhea, commercial oral rehydration solutions are usually needed. These solutions are available in packets for easy travel. People should try to consume enough fluids so that clear-to-light yellow urine is produced every 3 to 4 hours. While affected with dysentery, it is better to stick to a bland diet (bananas, rice, soda crackers, applesauce, toast) and avoid milk products.

Dysentery can be prevented to some extent by practising careful personal hygiene.

People who travel to or live in areas with high rates of dysentery should follow the following advice:

  • Do not eat any foods cooked in unhygienic circumstances, such as from street vendors.
  • Only eat cooked foods that have been heated to a high temperature. Do not eat cooked foods that have cooled.
  • Do not eat raw vegetables. Avoid species of fruits without peels. Open fruits with peels yourself.
  • Drink only commercially bottled or boiled water. Do not use ice unless it has been made from purified water.
  • Use only bottled or boiled water to wash and to cook food in, to wash hands, and to brush teeth.
  • Consider cleaning hands with an alcohol-based hand sanitizer.
  • Always use a condom for any sexual activity involving anal contact and wash carefully before and after sexual activity.
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