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Balantidiasis

[Balantidium coli]

Causal Agents

Balantidium coli, a large ciliated protozoan parasite.


Life Cycle

Life Cycle

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

Geographic Distribution

Worldwide. Because pigs are an animal reservoir, human infections occur more frequently in areas where pigs are raised. Other potential animal reservoirs include rodents and nonhuman primates.

Clinical Presentation

Most cases are asymptomatic. Clinical manifestations, when present, include persistent diarrhea, occasionally dysentery, abdominal pain, and weight loss. Symptoms can be severe in debilitated persons.

Balantidium coli cysts in wet mounts.

 

Both Balantidium coli trophozoites and cysts are found in stool. Trophozoites are characterized by: their large size (40 µm to 200 µm), the presence of cilia on the cell surface, a cytostome, and a bean shaped macronucleus which is often visible and a smaller, less conspicuous micronucleus. Cysts are seen less frequently and range in size from 50 µm to 70 µm. B. coli can also invade tissue.
Figure A

Figure A: B. coli cyst in a wet mount, unstained.

Figure B

Figure B: B. coli cyst in a wet mount, unstained.

Figure C

Figure C: B. coli cyst in a wet mount, unstained.

B. coli trophozoites.

Figure A

Figure A: B. coli trophozoite in a wet mount, 500× magnification. Note the visible cilia on the cell surface.

Figure B

Figure B: B. coli trophozoite under differential interference contract (DIC) microscopy, 500× magnification

Figure C

Figure C: B. coli trophozoite in a wet mount, 1000× magnification. Note the visible cilia on the cell surface. Image contributed by the Oregon Public Health Laboratory.

Figure D

Figure D: B. coli trophozoite in a Mann's hematoxylin stained smear, 500× magnification. Note the cytosome (black arrow) and the bean shaped macronucleus.

Balantidium coli trophozoites in intestinal tissue, stained with hematoxylin and eosin (H&E)

Figure A

Figure A: Balantidium coli trophozoites in colon tissue stained with hematoxylin and eosin (H&E)at 200x magnification.

Figure B

Figure B: Balantidium coli trophozoites in colon tissue stained with hematoxylin and eosin (H&E) at 400x magnification.

Figure C

Figure C: Balantidium coli trophozoites in tissue stained with H&E.

Laboratory Diagnosis

Diagnosis is based on detection of trophozoites in stool specimens or in tissue collected during endoscopy. Cysts are less frequently encountered. Balantidium coli is passed intermittently and once outside the colon is rapidly destroyed. Thus stool specimens should be collected repeatedly, and immediately examined or preserved to enhance detection of the parasite.

More on: Morphologic comparison with other intestinal parasites

Treatment Information

Three medications are used most often to treat Balantidium coli: tetracycline, metronidazole, and iodoquinol.

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

Tetracycline is available for human use in the United States.

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.

Pregnancy Category D: There is positive evidence of human fetal risk, but the benefits from use in pregnant women may be acceptable despite the risk (e.g., if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective).

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.

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 age 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

Metronidazole is available for human use in the United States.

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 in the first trimester is generally not advised.

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).

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.

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

Iodoquinol is available for human use in the United States.

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.

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

The safety of iodoquinol in children has not been established.

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DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.

  • Page last reviewed: October 17, 2016
  • Page last updated: October 17, 2016
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