NAME: Balantidium coli
SYNONYM OR CROSS REFERENCE: Balantidiasis Footnote 1.
CHARACTERISTICS: Balantidium coli is the largest and the only ciliated protozoan parasite of humans. B. coli is a member of the class Ciliata, order Trichomonatida and family Balantidiidae. The life cycle of B. coli consists of two stages: a ciliated trophozoite and an environmentally resistant cyst. Cysts are the infectious stage. Following the ingestion of infective cysts, excystation occurs in the small intestine and trophozoites become established in the mucosa of the terminal ileum and colon. The trophozoites are oblong, spheroid, or more slender, 30 to 150 µm in length by 25 to 120 µm in width. Cysts, which are most commonly found in stools, are spheroid or ovoid, measuring 40-60 µm in diameterFootnote 1Footnote 2. B. coli cells contain 1 large kidney bean shaped macronucleus, 1 rounded micronucleus, and 2 contractile vacuoles in the cytoplasm, and reproduction is by asexual division. Cells can be found in the anaerobic environment of the intestine and grow between 20°C and 40°C. Its body surface is covered with longitudinal cilia and movement is through rotation in the intestinal colon Footnote 3Footnote 4.
PATHOGENICITY/TOXICITY: The most common sites of B. coli infection (>95%) are the terminal ileum and colon, and specially the rectosigmoid area. B. coli is the only ciliated protozoon known to be pathogenic to humans Footnote 5 and infection of the gastrointestinal tract is often not serious and can be asymptomatic. B. coli infections are similar to amoebiasis in that a silent carrier state may be present. However, dysenteric symptoms can be observed in patients with malnutrition, alcoholism, or suppressed immune systems Footnote 4. Acute disease with fulminating balantidiosis is characterized by severe diarrhea and mucoid bloody stool, nausea, vomiting, headache, and has a 30% mortality rate Footnote 3Footnote 4. Chronic infections are manifested by non-bloody diarrhea, cramping and halitosis and abdominal pain secondary to trophozoite invasion of the large intestine. Protozoa that pass the submucosa may cause abscesses and hemorrhagic lesions that can eventually result in appendicitis and secondary infections from bacteria, such as uterine infections, vaginitis, and cystitis Footnote 3Footnote 4. The most severe symptoms of infection include anorexia, weight loss, tenesmus, bloody stools, intestinal hemorrhage and perforation. Severe infections are rare but can sometimes cause death in undernourished and immunocompromised populations Footnote 1.
EPIDEMIOLOGY: B. coli has a worldwide prevalence of 0.02-1%, thus it is not a common human pathogen despite its global distribution Footnote 4. It is more common in warm climates such as the tropics and subtropics, and regions with improper hygienic conditions. It is commonly found in China, Philippines, Middle East, Indonesia, Japan, South Pacific Islands, Brazil, Peru, Panama, and Cuba Footnote 5. High prevalence is observed in areas where close contact with pigs or pig feces is common such as farms and abattoirs. The rate of infection of pig farmers in New Guinea is 28% Footnote 6, and the rate of B. coli infections in the Altiplano area of Bolivia is between 6-29% Footnote 7. The disease has also been documented in asylums, orphanages, and prisons Footnote 4.
HOST RANGE: Humans Footnote 1Footnote 5Footnote 8, pigs Footnote 4, guinea-pigs, wild boars, horses, bovines, insects, fish, amphibians Footnote 8, rats, chimpanzees, orangutans, dogs, and cats Footnote 4.
INFECTIOUS DOSE: Unknown, it is estimated to be low Footnote 9.
MODE OF TRANSMISSION: The major risk factor for humans is close contact with pigs or pig feces Footnote 10. Transmission occurs most commonly through the fecal-oral route by the oral ingestion of protozoan cysts from contaminated food or direct contact with animals Footnote 5. Water is the primary disseminator of B. coli infections Footnote 4. Rats can be carriers of the pathogen however, it is not clear if transmission to humans is possible. Cockroachs may serve as a mechanical agent of transmission from feces to food Footnote 11 .
COMMUNICABILITY: Transfer of balantidiasis between humans is possible by the spread of B. coli cysts through fecal contamination of food or water supply Footnote 14, but occurrence is rare Footnote 5.
ZOONOSIS: Transfer to humans can result from close contact with, or handling of pigs, and occurs through the fecal oral-route Footnote 14.
DRUG SUSCEPTIBILITY: Susceptibility has been shown for tetracycline and metronidazole, which are the drugs of choice against infection. Iodoquinol, doxycycline, and nitazoxanide can be used as alternatives Footnote 4Footnote 5.
SUSCEPTIBILITY TO DISINFECTANTS: The protozoa can be disinfected with acid anionics, quaternary ammonium compounds, iodophores, and organic and inorganic hypochlorite compounds (i.e. 1% sodium hypochlorite) Footnote 15. The protozoa can be disinfected from water by chlorine, ozone, and carbon dioxide Footnote 15. However, chlorine, at the concentrations normally used for ensuring water safety, is not effective against cysts of Balantidium Footnote 4.
PHYSICAL INACTIVATION: The protozoa can be inactivated by heat, radiation, low temperature storage and desiccation Footnote 15.
SURVIVAL OUTSIDE HOST: The protozoa can be viable for weeks in pig feces when kept in moist form and away from sunlight, and can survive for 10 days in the environment Footnote 14. Trophic ciliates can survive in culture for 24-48 hours when kept higher than 40°C Footnote 4.
SURVEILLANCE: Cyst stages are more common in formed stools. Physical diagnosis includes examination of pig feces microscopically detecting ciliary movement Footnote 5 and histological examination of an intestinal biopsy Footnote 1. The protozoa can be detected through stool concentrates and serological methods Footnote 5. Methods for concentration of parasites from stool samples, making them easier to find, include sedimentation and flotation Footnote 16. Molecular biological methods such as PCR are another method of detecting B. coli Footnote 1.
Note: All diagnostic methods are not necessarily available in all countries.
LABORATORY-ACQUIRED INFECTIONS: None reported to date, risk of infection in the laboratory setting is considered to be low Footnote 4.
SOURCES/SPECIMENS: Feces and infected tissue samples from the intestine.
SPECIAL HAZARDS: Caution should be taken when handling porcine of human fecal samples as they may contain cysts.
RISK GROUP CLASSIFICATION: Risk Group 2.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 18.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 18.
SPILLS: Allow aerosols to settle and while wearing protective clothing, gently cover the spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working inwards towards the centre. Allow sufficient contact time before clean up Footnote 18.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism by autoclave, chemical disinfection, gamma irradiation, or incineration before disposing Footnote 18.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled Footnote 18.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Copyright © Public Health Agency of Canada, 2011 Canada