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Balantidiasis is an infectious disease produced by a single-celled microorganism (protozoan) called Balantidium coli that infects the digestive tract. It is primarily a disease of the tropics, although it is also found in cooler, temperate climates. Most persons with balantidiasis do not exhibit any noticeable symptoms (asymptomatic), but a few individuals will develop diarrhea with blood and mucus and an inflamed colon (colitis).


Balantidiasis is caused by Balantidium coli, a parasitic protozoan that infects the large intestine. B. coli is the largest and only protozoan, having cilia or hair-like structures, that is capable of causing disease in humans. Balantidiasis occurs most commonly in areas with poor sanitation and in settings where humans live in close contact with pigs, sheep, or goats.

Causes and symptoms

Balantidiasis is transmitted primarily by eating food or drinking water that has been contaminated by human or animal feces containing B. coli cysts. During its life cycle, this organism exists in two very different forms: the infective cyst or capsuled form, which cannot move but can survive outside the human body because of its thick, protective covering; and the disease-producing form, the trophozoite, which although capable of moving, cannot survive once excreted in the feces and, therefore, cannot infect others. In the digestive tract, the cysts are transported to the intestine where the walls of the cysts are broken open by digestive secretions, releasing the mobile trophozoites. Once released within the intestine, the trophozoites multiply by feeding on intestinal bacteria or by invading the lining of the large intestine. Within the lining of the large intestine, the trophozoites secrete a substance that destroys intestinal tissue and creates sores (ulcers) or abscesses. Trophozoites eventually form new cysts that are carried through the digestive tract and excreted in the feces. Under favorable temperature and humidity conditions, the cysts can survive in soil or water for weeks to months, ready to begin the cycle again.

Most individuals with balantidiasis have no noticeable symptoms. Even though these individuals may not feel ill, they are still capable of infecting others by person-to-person contact or by contaminating food or water with cysts that others may ingest, for example, by preparing food with unwashed hands.

The most common symptoms of balantidiasis are chronic diarrhea or severe colitis with abdominal cramps, pain, and bloody stools. Complications may include intestinal perforation in which the intestinal wall becomes torn, but the organisms do not spread to other parts of the body in the blood stream.


Diagnosis of balantidiasis, as with other similar diseases, can be complicated, partly because symptoms may or may not be present. A diagnosis of balantidiasis may be considered when a patient has diarrhea combined with a possible history of recent exposure to amebiasis through travel, contact with infected persons, or anal intercourse.

Specifically, a diagnosis of balantidiasis is made by finding B. coli cysts or trophozoites in the patient's stools or by finding trophozoites in tissue samples (biopsy) taken from the large bowel. A diagnostic blood test has not yet been developed.

Stool examination

This test involves microscopically examining a stool sample for the presence of cysts and/or trophozoites of B. coli.


To take a tissue sample from the large intestine, a procedure called a sigmoidoscopy is performed. During a sigmoidoscopy, a thin, flexible instrument is used to visually examine the intestinal lining and obtain small tissue specimens.


Patients with balantidiasis are treated with prescription medication, typically consisting of a ten day course of either tetracycline or metronidazole. Alternative drugs that have proven effective in treating balantidiasis include iodoquinol or paromomycin.


Asymptomatic Persons who carry a disease and are usually capable of transmitting the disease but who do not exhibit symptoms of the disease are said to be asymptomatic.

Biopsy The removal of a tissue sample for diagnostic purposes.

Ciliated Covered with short, hair-like protrusions, like B. coli and certain other protozoa. The cilia or hairs help the organism to move.

Colitis An inflammation of the large intestine that occurs in some cases of balantidiasis. It is marked by cramping pain and the passing of bloody mucus.

Protozoan A single-celled, usually microscopic organism, such as B. coli, that is eukaryotic and, therefore, different from bacteria (prokaryotic).

Sigmoidoscopy A procedure in which a thin, flexible, lighted instrument, called a sigmoidoscope, is used to visually examine the lower part of the large intestine.


Although somewhat dependent on the patient's overall health, in general, the prognosis for most patients with balantidiasis is good. Severely infected patients occasionally die as a result of a tear in the intestinal wall (intestinal perforation) and consequent loss of blood.


There are no immunization procedures or medications that can be taken prior to potential exposure to prevent balantidiasis. Moreover, people who have had the disease can become reinfected. Prevention requires effective personal and community hygiene. Specific safeguards include the following:

  • Purification of drinking water. Water can be purified by filtering, boiling, or treatment with iodine.
  • Proper food handling. Measures include protecting food from contamination by flies, cooking food properly, washing one's hands after using the bathroom and before cooking or eating, and avoiding foods that cannot be cooked or peeled when traveling in countries with high rates of balantidiasis.
  • Careful disposal of human feces.
  • Monitoring the contacts of balantidiasis patients. The stools of family members and sexual partners of infected persons should be tested for the presence of cysts or trophozoites.



Goldsmith, Robert S. "Infectious Diseases: Protozoal & Helminthic." In Current Medical Diagnosis and Treatment, 1998, edited by Stephen McPhee, et al., 37th ed. Stamford: Appleton & Lange, 1997.

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Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues



Ingestion of the protozoan parasite Balantidium coli causes balantidiasis (ba-lan-ti-DYE-a-sis) infection. This parasite is transmitted from animal reservoirs to humans by oral contact with fecal matter. This transmission occurs when unwashed food or unclean water is ingested, or if hands are not washed after handling animals. While balantidiasis infection is rare, and most cases are asymptomatic, some cases result in diarrhea, dysentery, colitis, abdominal pain, weight loss, and fatalities. Treatment is effective and involves a short course of antibiotics, which eradicates the parasite.

Balantidiasis occurs worldwide, but is more common in areas in which humans live in close contact with live-stock, and particularly in areas with poor sanitation or other health problems. Infection is best prevented by treating water, washing food and hands, and reducing contact with livestock. Improving community sanitation standards, as well as educating communities on the importance of sanitation, can also help reduce infection.


RESERVOIR: The animal or organism in which the virus or parasite normally resides.

TROPHOZOITE: The amoeboid, vegetative stage of the malaria protozoa.

Disease History, Characteristics, and Transmission

Balantidiasis is an intestinal infection caused by the parasite Balantidium coli. Humans are infected when they ingest B. coli cysts—immobile, protected forms of the parasite. Once in the body, these cysts break open and a mobile stage called a trophozoite is released. The trophozoite feeds on bacteria within the intestine, or enters the intestinal lining and secretes a tissue-destroying substance. As a result, sores (ulcers) and abscesses develop in the intestinal lining. New cysts are formed by the trophozoites and are excreted from the body in the feces. The cysts are well-protected and can remain outside the body under favorable conditions for many weeks.

B. coli are transmitted to humans from animal reservoirs such as livestock, rodents, and non-human primates. The most common reservoirs are pigs, which are often infected with B. coli, but tend to be asymptomatic. Transmission occurs when humans ingest food or water contaminated with the feces of infected animals, or when the mouth comes in contact with something contaminated with feces, such as unwashed hands.

Balantidiasis infection is uncommon in humans, and most cases are asymptomatic. However, asymptomatic humans are still capable of spreading the infection. When symptoms do appear, the most common symptoms are diarrhea, dysentery, abdominal cramps, and inflammation of the colon. In severe cases, perforation of the intestinal wall may occur, which can be fatal.

Scope and Distribution

Balantidiasis infection occurs worldwide, although it is more common in the tropics. It also is more common in regions where livestock, particularly pigs, is kept in conjunction with poor water systems and poor sanitation. Bolivia, the Philippines, and Papua New Guinea have all had outbreaks of balantidiasis, although the prevalence of the parasite B. coli is usually lower than 1%.

Treatment and Prevention

Medical treatment of balantidiasis is usually effective and is administered to both symptomatic and asymptomatic patients. Asymptomatic patients are treated in order to prevent them from spreading infection to others. Symptomatic patients are treated because untreated balantidiasis can become chronic and lead to dehydration, abdominal bleeding, and perforation of the intestinal wall, any of which—left untreated—can be fatal. Treatment usually involves oral administration of one of the following antibiotics: tetracycline, metronidazole, and iodoquinol. Tetracycline is the treatment of choice, but it is not recommended for pregnant women and children under the age of eight.

The most effective methods to prevent infection by B. coli involve improving sanitation. This includes boiling contaminated water prior to using it, washing hands after handling pigs or using the toilet, effectively washing and cooking food prior to eating, and preventing water sources from coming into contact with animal and human feces. As the most common mode of infection is from pigs to humans, reducing contact between pigs and humans will reduce infection. This can be achieved by preventing pigs from sharing human water sources, washing hands after handling pigs, and putting up barriers between pig and human living areas.

Impacts and Issues

Balantidiasis infection most commonly occurs in communities in which sanitation is poor. This situation often arises due to a lack of resources to provide adequate sanitation, as well as a lack of education about sanitary living. Infections by the parasite B. coli have also been found to cause more severe infection in people who are already debilitated. This may be due to malnourishment, coinciding parasitic infections, or a weakened immune system.

Efforts to improve sanitation and health in communities may lead to a reduction in the prevalence of infection. Installing hygienic measures such as potable water sources, toilets separate from living areas, and separate housing for livestock and humans will greatly reduce the likelihood of transmission of B. coli between animals and humans. In addition, educating people on the risks associated with poor hygiene may also help prevent transmission. Addressing other health issues within communities, such as coexisting parasitic infections and malnourishment, will help improve the overall health of the community and will aid in reducing the severity of any infections that do occur.

See AlsoDysentery; Handwashing; Parasitic Diseases; Sanitation.



Mandell, G.L., J.E. Bennett, and R. Dolin. Principles and Practice of Infectious Diseases. Vol. 2. Philadelphia, PA: Elsevier, 2005.

Web Sites

Centers for Disease Control and Prevention. “Balantidiasis.”

May 6, 2004. <> (accessed February 2, 2007).

Stanford University. “The Parasite: Balantidium coli. The Disease: Balantidiasis.” May 23, 2003. <> (accessed February 2, 2007).

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balantidiasis (bal-ăn-ti-dy-ă-sis) n. an infestation of the large intestine of humans with the parasitic protozoan Balantidium coli. The parasite invades and destroys the intestinal wall, causing ulceration and necrosis, and the patient may experience diarrhoea and dysentery.