Updated: Nov 28, 2018
Author: Valda M Chijide, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD 



Balantidiasis (also known as balantidiosis) is defined as large-intestinal infection with Balantidium coli, which is a ciliated protozoan (and the largest protozoan that infects humans). B coli is known to parasitize the colon, and pigs may be its primary reservoir. See the image below.

Trophozoite of Balantidium coli in colon. This pho Trophozoite of Balantidium coli in colon. This photograph shows the large macronucleus and the thin cell membrane covered with cilia (X820). Courtesy of Armed Forces Institute of Pathology (AFIP 75-9300).

See Common Intestinal Parasites, a Critical Images slideshow, to help make an accurate diagnosis. 


B coli exists as a trophozoite and a cyst and usually affects the large intestine, from the caecum to the rectum. The trophozoites replicate by binary fission and conjugation, and they subsist on bacteria. Humans ingest infective cysts, which then migrate to the large intestine, cecum, and terminal ileum. The organisms primarily dwell in the lumen but can also penetrate the mucosa and cause ulcers. B coli produces hyaluronidase, potentially enhancing its ability to invade the mucosa.[1]



United States

Balantidiasis is found worldwide and has an overall estimated prevalence of 1%. Balantidiasis epidemics have occurred in psychiatric hospitals in the United States.


Balantidiasis tends to be more common among persons who handle pigs. The disease is reported most commonly in Latin America; Southeast Asia; and Papua, New Guinea. In 1971, a balantidiasis outbreak involving 100 people occurred in Truk following a typhoon.[2] In France, a pork butcher with immunosuppression due to alcohol use developed occupational balantidiasis.[3]


Most cases of balantidiasis in immunocompetent individuals are asymptomatic. Mortality rates associated with acute and fulminating types of balantidiasis were as high as 30% in untreated patients prior to the introduction of antibiotics. Pneumonia has been described in patients with cancer-related immunosuppression[4] and has not always been associated with direct contact with pigs.


In the antibiotic era, severe balantidiasis carries an improved prognosis, and most affected patients now recover.

Patient Education

Patients should be counseled on the importance of good handwashing, particularly after being exposed to environments where likelihood of infection is high.




Potential symptoms of balantidiasis include the following:

  • Diarrhea (watery, bloody, mucoid)

  • Nausea

  • Vomiting

  • Abdominal pain

  • Anorexia

  • Weight loss

  • Headache

  • Mild colitis

  • Fever

  • Severe and marked fluid loss (resembling amebic dysentery)

  • Dysenteric syndrome[5, 6]


Patients with balantidiasis may present with abdominal tenderness, fever, and prolonged diarrhea, which may result in signs of dehydration.


Risk factors for balantidiasis include contact with pigs, handling fertilizer contaminated with pig excrement, and living in areas where the water supply may be contaminated by the excrement of infected animals. Poor nutrition, achlorhydria, alcoholism, and immunosuppression may also be contributing factors.


Intestinal perforation and extraintestinal spread to liver and mesenteric lymph nodes are rare.

Pulmonary involvement has been reported and appears to be more common in patients with underlying illnesses such as diabetes, cancer, or impaired lymphocyte function.



Differential Diagnoses



Laboratory Studies

Wet smear stool specimens

B coli does not stain well on permanent stained smears, complicating diagnosis of balantidiasis; however, the diagnosis can be made by examining wet smears of stool specimens or scrapings from the periphery of ulcers during an endoscopic examination.

On unstained specimens, the trophozoite is recognized by its large size (approximately 50-100 µm in length and 40-70 µm in width), a short ciliary covering, and its spiraling motility. It is frequently observed under low power. On stained preparations, the trophozoite characteristically shows 2 nuclei: the macronucleus, which is kidney-shaped, and the micronucleus, which is spherical and lies close to the macronucleus.

Cysts may be spherical or ellipsoid and are approximately 50-70 µm long. Newly encysted organisms observed on unstained specimens may still have cilia, but cilia disappear after a longer period of encystment. Observation of a macronucleus and a micronucleus is diagnostic if observed in a cyst on a stained specimen. See the images below.

Trophozoite of Balantidium coli in colon. This pho Trophozoite of Balantidium coli in colon. This photograph shows the large macronucleus and the thin cell membrane covered with cilia (X820). Courtesy of Armed Forces Institute of Pathology (AFIP 75-9300).
Cyst of Balantidium coli in feces. This photograph Cyst of Balantidium coli in feces. This photograph demonstrates a thick cyst wall and a large macronucleus (X820). Courtesy Armed Forces Institute of Pathology (AFIP 75-9301).

Imaging Studies

Chest radiography may show pulmonary parenchymal involvement in patients with balantidiasis.

Computed tomography (CT) scanning may reveal pulmonary parenchymal and lymph node involvement, as well as involvement of other organ systems.


Colonoscopy: Perform an endoscopic examination of the colon to obtain a biopsy of ulcers, thereby aiding in diagnosis of balantidiasis. Obtain the specimens from the periphery of ulcers.

Bronchoalveolar lavage (BAL) can identify organisms on wet mount of bronchial secretions.

Histologic Findings

B coli can invade the mucosa and submucosa, causing ulceration and infiltration with polymorphonuclear cells, lymphocytes, and eosinophils. Trophozoites can be observed at the invading edge of ulcers or at the periphery of submucosal abscesses.



Medical Care

Special attention should be paid to volume replacement and electrolyte repletion in patients with balantidiasis who have severe diarrhea.

Surgical Care

Balantidiasis rarely manifests as acute appendicitis, which requires appendectomy.[7]


Consult a surgeon for management of acute abdomen problems (eg, appendectomy, laparotomy).

Consult a gastroenterologist for patients who require colonoscopy.

Therapy in an intensive care unit may be required for patients with balantidiasis who show signs of clinical deterioration despite receipt of appropriate antibiotics.


A clean water supply and hygienic living conditions can prevent balantidiasis.

Avoiding contact with pigs and fertilizer that is contaminated with pig excrement can decrease the risk of balantidiasis.

Long-Term Monitoring

Patients with balantidiasis should have a follow-up visit after treatment to document the resolution of symptoms. Also, obtain a stool specimen and a wet smear to check for organisms.



Medication Summary

The goals of pharmacotherapy are to reduce morbidity and to prevent complications. Prolonged courses of therapy may be required to cure balantidiasis in patients who are infected with HIV or who are otherwise immunosuppressed.


Class Summary

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting. Tetracycline is the treatment of choice, with metronidazole being the primary alternative. Iodoquinol, puromycin, and nitazoxanide are also effective against balantidiasis.

Tetracycline (Sumycin)

Isolated from a strain of Streptomyces aureofaciens. Exerts a bacteriostatic effect by reversibly binding to 30S and 50S ribosomal subunits of susceptible organisms, thereby inhibiting protein synthesis.

Metronidazole (Flagyl)

Synthetic drug with antiprotozoal and antibacterial action used to treat symptomatic patients with diarrhea.

Iodoquinol (Yodoxin)

Contact amebicide works in the lumen of intestine.