Balantidiasis (Balantidium Coli Disease)

What is balantidiasis?

Balantidiasis refers to the protozoal infection of the large intestine, caused by Balantidium coli. Pigs may be the primary reservoir of this ciliated protozoan, which can also infect humans and infest the colon. B. coli transmits through the fecal-oral route and humans can acquire balantidiasis by ingesting contaminated food and water, which has come into contact with feces of infected humans or animals.

Many patients harboring B. coli infection do not present any symptoms, however, patients with other serious illnesses are more affected by balantidiasis. Such people may experience symptoms like persistent abdominal pain, diarrhea, and occasionally a perforated colon. Balantidiasis is rare in the United States, but is more common in the endemic tropical countries with warmer climates. B. coli is also more prevalent in developing countries with poor sanitation and hygiene practices.

How common is balantidiasis?

Balantidium infection in humans is rare in the United States. However, balantidiasis is more common among pigs in warmer regions, and in monkeys in the tropical climates, which is why human infections are also more common in these parts of the world. In United States, balantidiasis affects 1% population, and is more common among travelers and in people who handle pigs.

Infection with Balantidium Coli

Infection with the parasite can result in one of three manifestations :

  • Asymptomatic where the infected person does not exhibit any symptoms but excretes cyst.
  • Acute where there is inflammation of the colon (colitis) with intense symptoms such as bloody diarrhea.
  • Chronic where there is recurrent acute episodes but the patient is almost asymptomatic in between.

Trophozoites and cysts

B. coli protozoa exist in two forms: trophozoites or cysts. Trophozoites are oblong or spherical in shape, and are the largest known protozoan parasites of human. On the other hand, cysts or the infective forms of B. coli, cysts are smaller and more spherical in shape. Unlike trophozoites, cysts do not have cilia on their surface and are not motile.

Picture from Wikimedia Commons


Balantidiasis is transmitted to new hosts through cysts of B. coli by ingestion of contaminated food or water. Once the cysts reach the small intestine, the trophozoites escape from the cysts and colonize the large intestine. The trophozoites multiply in the lumen of the large intestine of humans and animals, and again form infective cysts. Mature, infective cysts are passed with feces and transmitted to new hosts.


Though B. coli resides in the lumen of the large intestine, they can affect the cecum and the rectum as well. These large protozoans can also penetrate the thick lining of the intestine called mucosa and cause ulcers. B. coli invade the mucosa with the help of the enzyme hyaluronidase that degrades components of mucosal cell wall.

Other bacteria present in the intestine may also enter the ulcer along with B. coli, resulting in secondary infections.

Signs and Symptoms

Majority of the people with B. coli infection do not present any symptoms. These people, however, may still act as B. coli carriers, in whom the protozoa reside and produce tiny infective cysts. These cysts passed in the feces result in more infections or re-infection. More severe signs and symptoms are seen in people with low immunity. Upon acquiring the infection, the following symptoms may include :

  • Abdominal pain
  • Diarrhea (watery or with blood or mucous)
  • Dysentery
  • Nausea
  • Weight loss
  • Vomiting
  • Headache
  • Low-grade fever
  • Loss of appetite
  • Fluid loss
  • Foul breath
  • Inflammation of the colon (colitis)
  • Presence of ulcers in the intestine
  • Perforation of the intestine (in advanced stages)

Many of these symptoms are non-specific and may be mistaken for other diseases.

Causes and Risk Factors

Balantidiasis spreads through ingestion of infective cysts of B. coli, present in contaminated water or food. Several factors that increase the risk for developing balantidiasis may include the following:

  • Close contact with pigs.
  • Handling manure or fertilizer contaminated with pig feces.
  • Living in areas with contaminated water supply.
  • Poor nutrition.
  • Absence of gastric acid (achlorhydria).
  • Alcoholism.
  • Poor or weaken immune system.

Tests and Diagnosis

Balantidiasis can be diagnosed with the help of following tests:

  • Lab tests: Stool samples are used to diagnose B. coli infection. The large-sized trophozoites of B. coli can be recognized easily, when the stool samples are smeared on a slide and watched under the microscope. Although the protozoa have cilia on their bodies, the cilia may always not be visible as the organisms lose them during prolonged periods in the cyst stage.
  • Colonoscopy: An endoscopic examination of the colon may be performed to obtain a biopsy sample of ulcers.


Treatment of balantidiasis aims to decrease the severity of the symptoms and to prevent complications. Patients with a weak immune system often require prolonged courses of therapy.


Antibiotics are given to kill the B. coli protozoa. Tetracycline or other alternatives like metronidazole, puromycin, iodoquinol, and nitazoxanide may be given to the patients with balantidiasis.

Tetracycline kills the protozoa by inhibiting protein synthesis in their cells, whereas the synthetic drug metronidazole has efficient anti-protozoal and antibacterial action. Both drugs are frequently given to the patients experiencing diarrhea.

  • Tetracycline tablets are given for 10 days, 4 times a day, an hour before or 2 hours after meals; however, it is not recommended for pregnant women.
  • Metronidazole tablets are given for 5 days, 3 times daily.
  • Alternatively, iodoquinol tablets are given for 20 days, 3 times daily, after meals.

Fluid and electrolyte replenishment is recommended for patients with severe diarrhea.


Surgery is needed in rare cases, when balantidiasis causes appendicitis. In such patients, appendix is removed in a surgical procedure called appendectomy.


The following simple measures can prevent balantidiasis:

  • Drinking and using clean water supply.
  • Maintaining hygienic living conditions.
  • Avoiding contact with pigs and fertilizer contaminated with pig feces.
  • Washing hands thoroughly with soap and warm water after using the toilet and before handling food.
  • Washing all fruits and vegetables with clean water.

Complications and Prognosis

Balantidiasis can present complications in patients with underlying illnesses like diabetes, cancer, or in those with weak immune system. Left untreated, balantidiasis can cause death in 30% cases. Most of the deaths can be attributed to dysentery and bleeding, which result in shock and death.

Overall health is a key deciding factor in estimating the prognosis of balantidiasis. However, balantidiasis carries a good prognosis if treated in time with appropriate antibiotics.

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