Last updated:
11/5/2025
Years published: 1986, 1993, 2000, 2009, 2025
NORD gratefully acknowledges Gioconda Alyea, MD (FMG), MS, National Organization for Rare Disorders, for assistance in the preparation of this report.
Balantidiasis is a rare infection caused by a parasite known as Balantidium coli (Neobalantidium coli or Balantioides coli).1
Many infected people have no symptoms or only mild diarrhea and abdominal discomfort,1,2 but others may have more severe symptoms and may become acutely ill with fever, nausea, vomiting, abdominal pain and bloody diarrhea similar of acute intestinal inflammation, such as amoebic dysentery.2-7 Some people can develop severe complications.
Balantidiasis is primarily associated with pigs, which serve as the main reservoir. It spreads through contaminated food or water, often in areas where hygiene is poor and pigs are present. Prevention hinges on clean water, proper sanitation and good hygiene. Early diagnosis and appropriate treatment are effective in managing the infection.1
Balantidium is a type of protozoa, which are a diverse group of single-celled organisms that can be parasites. They are the only ciliated protozoon known to infect humans. Balantidiasis is considered a neglected tropical zoonotic disorder. The transmission of zoonotic disease occurs at the human–animal interface through direct or indirect exposure of humans to animals, their products (i.e., meat, milk, eggs), the same vectors and/or sharing the same environment.8
For updated information about Balantidiasis please visit the Centers for Disease Control and Prevention (CDC) of United States.
In many people, infection with Balantidium coli causes no symptoms at all. This is especially true in healthy people, where the parasite may live in the large intestine without causing noticeable illness. However, in some people, particularly those with a weakened immune system or underlying health conditions, the infection can lead to a range of gastrointestinal symptoms, some of which may be severe.
The signs and symptoms of balantidiasis may include:1,7
In rare but serious cases, if the parasite invades the lining of the colon, it may lead to complications such as:1,5,7
Chronic infection is relatively uncommon and consists of intermittent episodes of abdominal pain and diarrhea.7 Disease in the lung (pulmonary hemorrhage), urinary bladder problems and bone infection (vertebral osteomyelitis) have been described in a few case reports.9-13 Keratitis, an inflammation of the cornea, the clear, protective outer layer of the eye, has also been described in one case.12
Balantidiasis is caused by a microscopic parasite called Balantidium coli. This parasite is primarily transmitted to humans through contact with pig feces or by consuming food or water that has been contaminated by infected fecal matter.1-7
After the parasite is ingested, its protective cyst form breaks open (excysts) in the small intestine, releasing active forms known as trophozoites. These then travel to the large intestine, where they live in the intestinal lining and appendix. In this environment, they multiply by a process called binary fission and may occasionally exchange genetic material through a process called conjugation. Some of these trophozoites become cysts again, making them capable of infecting others. Others may invade the wall of the colon, leading to ulcers and damage to the tissue. Some of the organisms eventually return to the intestinal cavity and break down. The mature cysts are passed out of the body in feces, allowing the cycle of infection to continue.¹
In addition to pigs, rats and other animals such as camels, cattle, donkey, sheep and goats can also carry and spread the infection and may also be reservoirs for human infection. Animal fecal contamination of water or food consumed by humans is the principal means of infection by humans. Person-to-person transmission has rarely been reported, particularly in environments with poor sanitation.1,3,7
As commented above, Balantidium coli spreads via the fecal-oral route, which means infection can occur when a person consumes food or water contaminated with feces from infected animals or humans. Common ways infection can occur include:14
People with a weakened immune system, poor nutritional status, or underlying health conditions are at higher risk of developing more severe illness.7,14
Human balantidiasis occurs worldwide. It is rare in United States, but it is not systematically tracked. It is most prevalent in tropical and subtropical regions, including Latin America, the Philippines, Papua New Guinea and the Middle East (regions such as Brazil, New Guinea and southern Iran). Balantidiasis affects males and females equally. B. coli generally occurs among domestic and wild mammals, especially among pigs in warmer climates and monkeys in the tropics. Infection in humans is, therefore, also more common in pig farmers and pig-raising regions, especially in settings where hygiene is poor.1,3,7,14
Balantidiasis primarily spreads in poor, rural areas where people live in close contact with pigs and lack proper waste disposal. Infected swine shed cysts in their feces, contaminating water sources and facilitating transmission. Though rare in the U.S., a study at a mental hospital found a 5% infection rate, linked to poor hygiene and behaviors like eating dirt and eating feces (coprophagy).15
Balantidiasis is diagnosed by identifying the parasite Balantidium coli in a stool sample or in tissue taken from the lining of the colon during procedures such as a colonoscopy or sigmoidoscopy.7 Stool samples are examined under a microscope to detect the presence of B. coli.15 Doctors look for two forms of the parasite, trophozoites, which are the active, moving form, and cysts, which are the protective, non-motile form. Trophozoites are relatively large, ranging from 40 to 200 microns.3,7 They are more commonly seen in people with diarrhea, while cysts are more often found in stools that have a normal consistency.7 In more complex cases, scraping ulcers for tissue samples can help identify the parasite.7 Stool specimens should be collected repeatedly, and immediately examined or preserved to enhance detection of the parasite.1
Treatment
The most commonly used treatment is tetracycline (500 mg orally four times daily for 10 days), which is considered effective.1,7 If tetracycline is contraindicated, such as in cases of allergy, alternative treatments include metronidazole (750 mg orally three times daily for five days) or iodoquinol.7,14 Other medication like tinidazole and paromomycin have also been used based on their efficacy against similar protozoal infections.7
While combination therapies have been tried, no data support improved outcomes. Treatment is generally recommended for symptomatic patients. For asymptomatic individuals shedding cysts, treatment may still be indicated. Management of asymptomatic carriers should be individualized, particularly in settings where transmission risk is high. If symptoms persist, follow-up stool examinations are warranted.7
Preventive measures include access to clean water, proper disposal of human and animal feces, protection of water sources from animal contamination and good hand hygiene. Isolation of infected individuals isn’t necessary, but safe disposal of feces is critical to avoid contamination of food and water. Travelers should follow standard food and water safety precautions.7,14
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: [email protected]
Some current clinical trials also are posted on the following page on the NORD website:
https://rarediseases.org/living-with-a-rare-disease/find-clinical-trials/
For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com
For information about clinical trials conducted in Europe, contact:
https://www.clinicaltrialsregister.eu/
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Learn more https://rarediseases.org/patient-assistance-programs/medicalert-assistance-program/Ensuring that patients and caregivers are armed with the tools they need to live their best lives while managing their rare condition is a vital part of NORD’s mission.
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Learn more https://rarediseases.org/patient-assistance-programs/caregiver-respite/The information provided on this page is for informational purposes only. The National Organization for Rare Disorders (NORD) does not endorse the information presented. The content has been gathered in partnership with the MONDO Disease Ontology. Please consult with a healthcare professional for medical advice and treatment.
The Genetic and Rare Diseases Information Center (GARD) has information and resources for patients, caregivers, and families that may be helpful before and after diagnosis of this condition. GARD is a program of the National Center for Advancing Translational Sciences (NCATS), part of the National Institutes of Health (NIH).
View reportOrphanet has a summary about this condition that may include information on the diagnosis, care, and treatment as well as other resources. Some of the information and resources are available in languages other than English. The summary may include medical terms, so we encourage you to share and discuss this information with your doctor. Orphanet is the French National Institute for Health and Medical Research and the Health Programme of the European Union.
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