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Contributors: Carlos Seas MD, James H. Willig MD, MSPH
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Balantidiasis is a zoonotic disease caused by Balantidium coli, the largest enteric and only ciliate protozoan parasite that affects humans. Symptomatic balantidiasis affects the large intestine, causing dysentery that rarely complicates with intestinal bleeding, intestinal perforation, or extra-intestinal involvement.

Balantidium coli are mainly asymptomatically harbored by pigs in their large intestines, but other mammals such as nonhuman primates and boars can also serve as reservoirs. It has worldwide distribution but is more commonly reported in tropical and subtropical developing countries, in particular the Philippines, Papua New Guinea (reported prevalence of 28% among pig farmers), the Middle East, and several Latin American countries (prevalence 6%-29% Altiplano region of Bolivia). It is very seldom found and reported in developed countries.

The life cycle is very simple with only 2 stages: 1) a cystic infective stage and 2) an invasive trophozoite that infects the entire large intestine from cecum to rectum. The cyst has a thick wall that protects it from desiccation and allows its survival for at least 2 weeks at room temperature. Trophozoites are very sensitive to temperature and can only be observed in readily processed stool samples or in tissue sections.

Humans get the infection by ingesting cysts, usually from contaminated water sources or less commonly from contaminated food. Human-to-human transmission has been anecdotally reported, but it is possible in the setting of asylums, orphanages, mental health institutions, and prisons where poor hygiene may spread the infection easily.

Three clinical manifestations can occur:
  1. Asymptomatic infections are the most predominant form of infection. Repeated infections since childhood may protect individuals living in endemic areas from developing symptomatic disease. Interestingly, attempts at infecting humans have not been successful, indicating that even among exposed persons, symptomatic disease is infrequent.
  2. Chronic nonbloody diarrhea accompanied by nonspecific abdominal symptoms.
  3. Acute dysentery with tenesmus and abdominal pain is the classic yet infrequent form of presentation. Rarely, patients with this presentation may progress to a fulminant clinical course with intestinal bleeding and/or intestinal perforation, both associated with mortality above 30%. Extra-intestinal manifestations have been very rarely reported, including necrotizing pulmonary involvement, which may result from bloodstream dissemination or trans-diaphragmatic spread; genitourinary infections, including vaginitis, uterine infections and cystitis, which may result from direct spread from the anal area or from rectovaginal fistula; and vertebral osteomyelitis and myelitis, which result from hematogenous spread. Liver abscess is not a common manifestation of extra-intestinal involvement in contrast to what occurs in patients infected with Entamoeba histolytica.
Risk factors include close contact with pigs and living in endemic tropical or subtropical areas. Host factors that predispose to intestinal and extra-intestinal manifestations are malnutrition, alcohol use disorder, hypochlorhydria, concomitant helminthic infections, and immunosuppressive conditions including HIV/AIDS, use of steroids, and chemotherapy for cancer.


A07.0 – Balantidiasis

57725006 – Balantidiasis

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Differential Diagnosis & Pitfalls

Bacterial causes of dysentery, including infections by Shigella, Salmonella, invasive strains of Escherichia coli, and Campylobacter, and dysentery caused by E. histolytica.

There are no clinical manifestations or clinical findings that help distinguish among these entities. Stool examination is needed to make the diagnosis.

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Last Updated: 06/07/2018
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Balantidiasis (Acute Colitis) : Abdominal pain, Bloody diarrhea, Nausea, Vomiting, Contaminated food exposure, Contaminated vegetable exposure, Contaminated drinking water exposure, Weight loss, Tenesmus
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