Key points

• Balantidium coli is an intestinal parasite that causes the infection balantidiasis.
• Symptoms can include diarrhea and abdominal pain.
• You can get balantidiasis by consuming food or water contaminated with infective feces.

Overview

Balantidium coli is an intestinal protozoan parasite that causes the infection called balantidiasis. While this type of infection is uncommon in the United States, humans and other mammals can become infected with Balantidium coli by ingesting infective cysts from food and water that is contaminated by feces. Mostly asymptomatic, Balantidium infection can cause such symptoms as diarrhea and abdominal pain.

Balantidium coli infection in humans is rare in the United States. Balantidium coli is found throughout the world, but it is most prevalent in tropical and subtropical regions and developing countries. Because pigs are an animal reservoir, human infections occur more frequently in areas where pigs are raised, especially if good hygiene is not practiced.

Signs and symptoms

Most people infected with Balantidium coli experience no symptoms. Balantidium coli infects the large intestine in humans and produces infective microscopic cysts that are passed in the feces, potentially leading to re-infection or infection of others. People compromised immune systems are the most likely to experience more severe signs and symptoms. These include persistent diarrhea, dysentery, abdominal pain, weight loss, nausea, and vomiting. If left untreated, perforation of the colon can occur.

How it spreads

Balantidium coli is transmitted through the fecal-oral route. Humans can become infected by eating and drinking contaminated food and water that has come into contact with infective animal or human fecal matter. Infection can occur in several ways, including the following examples:

• Eating meat, fruits, and vegetables that have been contaminated by an infected person or contaminated by fecal matter from an infected animal,
• Drinking and washing food with contaminated water, or
• Having poor hygiene habits.

Prevention

Balantidium coli infection can be prevented when traveling by following good hygiene practices. Wash your hands with soap and warm water after using the toilet, changing diapers, and before handling food. Teach children the importance of washing hands to prevent infection. Wash all fruits and vegetables with clean water when preparing or eating them, even if they have a removable skin.

Testing

Stool samples can be examined by a laboratory. Microscopic examination can detect Balantidium coli in the stool.

Treatment

The three medications often used to treat Balantidium coli are tetracycline, metronidazole, and iodoquinol. See your healthcare provider for treatment.

Causal Agents

Balantidium (=Neobalantidium) (=Balantioides) coli, a large ciliated protozoan, is the only ciliate known to be capable of infecting humans. It is often associated with swine, the primary reservoir host. Recent molecular analyses have suggested the need for taxonomic revision, and it is now sometimes referred to as Neobalantidium coli or Balantioides coli, although this nomenclature has neither been resolved nor widely adopted in the medical community.

Life Cycle

Cysts are the stage responsible for transmission of balantidiasis (1). The host most often acquires the cyst through ingestion of contaminated food or water (2). Following ingestion, excystation occurs in the small intestine, and the trophozoites colonize the large intestine (3). The trophozoites reside in the lumen of the large intestine and appendix of humans and animals, where they replicate by binary fission, during which conjugation may occur (4). Trophozoites undergo encystation to produce infective cysts (5). Some trophozoites invade the wall of the colon and multiply, causing ulcerative pathology in the colon wall. Some return to the lumen and disintegrate. Mature cysts are passed with feces.

Hosts

Swine are the primary reservoir hosts. Humans can also be reservoirs, and other potential animal hosts include rodents and nonhuman primates.

Geographic Distribution

Balantidium coli occurs worldwide. Because pigs are the primary reservoir, human infections occur more frequently in areas where pigs are raised and sanitation is inadequate.

Clinical Presentation

Most cases are asymptomatic. Clinical manifestations, when present, may be acute or chronic with abdominal symptoms. Complications of associated diarrhea or dysentery can occur in protracted infections. Symptoms may be severe or fatal in debilitated/immunocompromised persons.

Extraintestinal infection is rare but potentially serious and typically occurs secondary to intestinal infection. Peritonitis and liver abscesses have been noted following intestinal perforation or rupture of fulminant colonic ulcers. Invasion of urogenital tract may be caused by contamination from the anal region or through fistulae caused by severe infection.

At a glance

• The three medications used to treat Balantidium coli infection include tetracycline, metronidazole, and iodoquinol.
• All three medications are available for human use in the United States.
• Consider safety precautions of medications in select populations.

Medication options

Tetracycline*: adults, 500 mg orally four times daily for 10 days; children ≥ 8 years old, 40 mg/kg/day (max. 2 grams) orally in four doses for 10 days. (Note: Tetracyclines are contraindicated in pregnancy and in children 8 years old. Tetracycline should be taken 1 hour before or 2 hours after meals or ingestion of dairy products.)

Alternatives

Metronidazole*: adults, 500-750 mg orally three times daily for 5 days; children, 35-50 mg/kg/day orally in three doses for 5 days.

OR

Iodoquinol*: adults, 650 mg orally three times daily for 20 days; children, 30-40 mg/kg/day (max 2 g) orally in three doses for 20 days. (Note: iodoquinol should be taken after meals.)

Nitazoxanide*: has been tried in small studies, which suggest some therapeutic benefit (adults, 500 mg orally twice daily for 3 days; children age 4-11 years old 200 mg orally twice daily for 3 days; children 1-3 years old 100 mg orally twice daily for 3 days).

*Not FDA-approved for this indication

• Tetracycline, metronidazole, and iodoquinol are available for human use in the United States.

Treatment precautions

Tetracycline

Note on treatment in pregnancy

Tetracycline is in pregnancy category D. Tetracycline should not be used in pregnant women due to positive evidence of maternal and fetal risk. Use during pregnancy should be limited to instances when there are contraindications to the use of other appropriate antibiotics and the potential benefit justifies the known risk.

Note on treatment during lactation

Tetracycline is excreted in breast milk. The American Academy of Pediatrics and the World Health Organization (WHO) both classify tetracycline as compatible with breast-feeding, although data on the use of tetracycline during lactation is limited. Tetracycline should be used during lactation only if the potential benefit of therapy to the mother justifies the known risk to the infant.

Note on treatment in pediatric patients

Tetracycline is contraindicated in children age 8 and younger as it may cause permanent discoloration of the teeth. The safety of intravenous tetracycline has not been established. Use of tetracycline in children aged 8 and younger should be limited to instances when there are contraindications to the use of other appropriate antibiotics and the potential benefit justifies the known risk.

Metronidazole

Note on treatment in pregnancy

Metronidazole is in pregnancy category B. Data on the use of metronidazole in pregnant women are conflicting. The available evidence suggests use during pregnancy has a low risk of congenital anomalies. Metronidazole may be used during pregnancy in those patients who will clearly benefit from the drug, although its use should be weighed against any potential risks.

Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).

Note on treatment during lactation

Metronidazole is excreted in breast milk. The American Academy of Pediatrics classifies metronidazole as a drug for which the effect on nursing infants is unknown but may be of concern. The World Health Organization (WHO) advises to avoid metronidazole treatment in lactating women. Metronidazole should be used during lactation only if the potential benefit of therapy to the mother justifies the potential risk to the infant.

Note on treatment in pediatric patients

The safety of metronidazole in children has not been established. Metronidazole is listed as an antiamebic and antigiardiasis medicine on the WHO Model List of Essential Medicines for Children, intended for the use of children up to 12 years of age.

Iodoquinol

Note on treatment in pregnancy

Oral iodoquinol has not been assigned a pregnancy category by the Food and Drug Administration. Data on the use of iodoquinol in pregnant women are limited, and risk to the embryo-fetus is unknown. Iodoquinol should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Note on treatment during lactation

It is not known whether iodoquinol is excreted in breast milk. Iodoquinol should be used with caution in breastfeeding women.

Note on treatment in pediatric patients

The safety of iodoquinol in children has not been established.