What Is Balantidiasis

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Balantidium. coli, carried by pigs, can transmit balantidiasis to humans through contaminated food or water. The severity of the disease can vary, with some cases showing no symptoms, while others can be life-threatening. Effective treatments exist, but disease prevention relies on clean water access and public health measures.


Balantidiasis is a relatively infrequent gastrointestinal infection caused by the trophozoite stage of the Balantidium coli (B.coli) parasite. This single-celled ciliated protozoan is commonly found in pigs but can, on rare occasions, infect humans. Notably, it is the largest ciliated protozoan known to affect humans.

This intestinal pathogen is found globally, particularly in regions with pig farming. It mainly affects developing nations where contaminated water sources are common. In urban areas, B. coli can also act as an opportunistic parasite in immunocompromised individuals, even without direct pig-related factors.1 In those individuals who become infected, the symptoms can vary widely. Some may remain asymptomatic or experience only mild diarrhoea and abdominal discomfort, while others may suffer more severe symptoms similar to acute intestinal inflammation. The clinical symptoms of balantidiasis may have similarities to those of other infections that also induce inflammation in the intestines, such as amoebic dysentery.1

In this article, we take a closer look at B. coli, the microscopic parasite responsible for balantidiasis in humans. We'll investigate its transmission, potential severity, available treatments, and essential preventive measures to reduce the risk of infection. Deepen your knowledge of this rare disease and its distinct characteristics.


Pigs are the primary reservoir hosts for B.coli. Furthermore, this parasite can be found in the large intestine of humans, as well as non-human primates such as chimpanzees, monkeys, and new-word monkeys. It can be also detected in wild rats and both domestic and wild hawks.2 

Some people with a weakened immune system (Immunocompromised) have developed balantidiasis without any direct pig contact; rats or contaminated food may be potential sources of infection.1 

Transmission and pathogenic mechanisms

B. coli is transmitted through the faecal-oral route, and humans can become infected by consuming food and drinks contaminated with infectious human or animal faeces. Infection can occur through various scenarios, including the following:

  •   Consuming meat, fruits, and vegetables that have been in contact with an infected individual or contaminated with faecal matter from an infected animal
  •   Ingesting and using water for food preparation that is contaminated
  •   Developing infection due to poor personal hygiene practices (CDC)

B. coli follows a straightforward life cycle, transitioning from a dormant cyst to an active trophozoite, and then back to a cyst. Transmission occurs directly from contaminated water or food to humans. No additional host, as required by many other parasites, is necessary.

The cysts are responsible for causing the infection. Once ingested, they release trophozoites through a process called excystation, which invade the colon's lining, multiply, and establish colonies.

Within the tissues, B. coli multiplies creates ulcers, and generates abscesses (a build of pus) that can reach the muscle layer. This invasion of the colonic tissue triggers a reaction from immune cells, including lymphocytes and eosinophils, leading to the death of epithelial cells due to reduced blood supply, a condition known as ischemic necrosis.2 

Clinical presentation

 B. coli infections can manifest clinically in several ways:

  • Asymptomatic carrier (most common): Individuals are infected but do not exhibit signs of illness.
  • Chronic symptomatic: Patients may experience alternating diarrhoea, constipation, and general abdominal discomfort.
  • Acute form: Patients with the acute form often present bloody stools, upper abdominal pain, weight loss, and dehydration.
  • Fulminant form (extremely severe with rapid progression): This can result in substantial gastrointestinal bleeding, severe dehydration, and shock.2 

While the intestine is the primary site of B. coli infection, the parasite can also cause infections in other areas of the body outside of the intestine such as the appendix, liver and lung.1,2

Affected populations

B. coli is found throughout the world, but it is most common in tropical and subtropical regions and developing countries. The disease is considered rare, affecting fewer than 1% of the human population.3

In rural and certain developing areas, where water sources may be contaminated with both pig and human waste, there's a higher chance of people getting the disease. This risk is more elevated in areas where pigs are raised and proper hygiene practices are not followed.1 

Laboratory diagnosis

Diagnosis is based on identifying rapidly mobile trophozoites in fresh stool samples from symptomatic patients or in tissues obtained during endoscopy. Cysts are less commonly found. B. coli is shed irregularly and deteriorates rapidly once outside the colon.4 To enhance parasite detection, stool specimens should be collected on multiple occasions, examined promptly, or preserved. Concentration techniques like sedimentation or flotation can improve recovery. The use of Lugol's iodine staining (a contrast dye) which is occasionally used, may obscure internal morphological details (CDC).


Tetracycline is the treatment of choice, with metronidazole and iodoquinol as alternative options. Some evidence suggests that Nitazoxanide, a broad-spectrum antiparasitic, may also be an effective treatment. HIV-infected individuals may require treatment courses lasting up to 20 days for complete resolution of the disease.4

Fortunately, the antimicrobial treatment for balantidiasis works well, and there haven't been any reports of resistance to these medications.1 

Microscopic description

Trophozoites and cysts of B. coli appear sizable and easily distinguishable when observed through an optical microscope at 10-40× magnification. The vegetative cells, which are the active and functioning cells of the organism as opposed to their spore forms, typically display gradual, helical movement, and they have an ovoid or pear-shaped appearance, measuring up to 150 μm in length, with cilia covering their entire cell surface. The cytostome, a mouth-like structure, is situated near the lower part. Cysts have a spherical or slightly ovoid shape, measuring around 50 μm in diameter, and each cyst contains a single cell. In both trophozoites and cysts, you can observe an elongated or bean-shaped macronucleus, with a small micronucleus that, in most cases, is not visible.5 

How can I prevent B.coli?

Preventing B. coli infection while travelling can be achieved by maintaining good hygiene practices.

 It's important to:

  •  Wash your hands with soap and warm water after using the toilet, changing diapers, and before touching food
  • Teach children about the significance of handwashing to avoid infection
  •  Wash all fruits and vegetables thoroughly with clean water when preparing or consuming them, even if they have a peel that can be removed (CDC)

Good hygiene, clean water, and robust public health measures are crucial to prevent this infection, which can persist as long as pigs exist. Balantidiasis can be avoided when these measures are in place.1 


Balantidium coli, commonly associated with pigs, can transmit balantidiasis to humans when they ingest contaminated food or water containing the parasite's cysts. The severity of this infection varies, with cases ranging from asymptomatic to life-threatening. The treatment for balantidiasis typically involves antibiotics, with tetracycline being the preferred choice, while alternative treatments include metronidazole and iodoquinol. Notably, these medications have shown high effectiveness, with no reported instances of resistance. This intestinal protozoan is distributed globally, particularly in regions where water sources may be contaminated with pig or human waste. It's important to note that immunocompromised individuals can contract the disease without direct pig contact, possibly through rats or contaminated food. Balantidiasis is a preventable disease when clean water and a robust public health infrastructure are in place, emphasizing the importance of sanitation and hygiene in disease prevention.


  • 2023 Oct 24]. Available from: https://www.cdc.gov/parasites/balantidium/faqs.html
  • Balantidiasis [Internet]. 2019 [cited 2023 Oct 24]. Available from: https://www.cdc.gov/dpdx/balantidiasis/index.html
  • Schuster FL, Ramirez-Avila L. Current world status of balantidium coli. Clin Microbiol Rev [Internet]. 2008 Oct [cited 2023 Oct 21];21(4):626–38. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2570149/
  • Sharma S, Harding G. Necrotizing lung infection caused by the protozoan Balantidium coli. Can J Infect Dis [Internet]. 2003 [cited 2023 Oct 22];14(3):163–6. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2094932/
  • Esteban JG, Aguirre C, Angles R, Ash LR, Mas-Coma S. Balantidiasis in Aymara children from the northern Bolivian Altiplano. Am J Trop Med Hyg. 1998 Dec;59(6):922–7. Available from: https://pubmed.ncbi.nlm.nih.gov/9886201/
  • Suh KN, Kozarsky P, Keystone JS. 285 - cyclospora cayetanensis, cystoisospora (Isospora) belli, sarcocystis species, balantidium coli, and blastocystis species. In: Bennett JE, Dolin R, Blaser MJ, editors. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases (Eighth Edition) [Internet]. Philadelphia: W.B. Saunders; 2015 [cited 2023 Oct 23]. p. 3184-3191.e2. Available from: https://www.sciencedirect.com/science/article/pii/B978145574801300285X
  • García-Rodríguez JJ, Köster PC, Ponce-Gordo F. Cyst detection and viability assessment of Balantioides coli in environmental samples: Current status and future needs. Food Waterborne Parasitol [Internet]. 2022 Jan 5 [cited 2023 Oct 23];26:e00143. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8802839/

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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