INTRODUCTION — Balantidium coli is the largest protozoan and the only ciliate parasite that infects humans [1,2].
EPIDEMIOLOGY — Human balantidiasis occurs worldwide; it is most prevalent in tropical and subtropical regions. 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 those areas, especially in settings where hygiene is poor. Camels, cattle, donkey, sheep, and goat may also be reservoirs for human infection [3]. Animal fecal contamination of water or food consumed by humans is the principal means for acquisition of infection by humans [4-6]. Transmission between humans can occur via the fecal-oral route.
Transmission of balantidiasis occurs via ingestion of cysts (figure 1). Following ingestion, excystation occurs in the small intestine, and the trophozoites colonize the large intestine. The trophozoites reside in the lumen of the large intestine of humans and animals, where they replicate by binary fission; conjugation may also occur. Trophozoites undergo encystation to produce infective cysts. Some trophozoites invade the wall of the colon and multiply; some return to the lumen and disintegrate. Mature cysts are passed in the stool and can remain viable for up to two weeks in the environment [7]. Cysts are considered the main infective stage; trophozoites can also be passed in stool but generally disappear soon after passage [3].
CLINICAL MANIFESTATIONS — Three forms of B. coli infection can occur: asymptomatic cyst excretion, acute colitis, and chronic infection [8-11]. Most cases are asymptomatic; patients with comorbidities (particularly immunosuppression) or other infections are at increased risk for developing symptomatic infection [12-14].
In sporadic cases with acute clinical manifestations, symptoms include nausea, vomiting, diarrhea, weight loss, and abdominal pain. Stools may be either watery or dysenteric [10]. Fulminant disease is rare and is most frequently associated with fulminating dysentery with or without multiple intestinal perforations. When present, the colonic ulcers and clinical presentation are similar to those found in amebic dysentery with deep invasion of the submucosa with organisms. Microperforations with resulting sepsis can be a potentially fatal complication.
Chronic infection is relatively uncommon; it consists of intermittent episodes of abdominal pain and diarrhea [3,11].
Rarely, extraintestinal disease occurs; spread to the peritoneal cavity, appendix, genitourinary tract, lung, and bone has been described [15-17]. Keratitis has also been described [18].
DIAGNOSIS — The diagnosis of intestinal B. coli infection is established by detection of trophozoites (picture 1) or cysts (picture 2) in stool examinations or mucosal scrapings obtained at colonoscopy or sigmoidoscopy [19]. The trophozoites are relatively large (40 to 200 microns). Stool trophozoites are more frequently observed in the setting of diarrhea, and stool cysts are more commonly observed in patients with stool of normal consistency [3].
DIFFERENTIAL DIAGNOSIS
●Amebic colitis – Clinical manifestations of amebic colitis range from mild diarrhea to severe dysentery, abdominal pain, weight loss, and occasionally fulminant colitis. The diagnosis is established via stool microscopy or colonic biopsy. (See "Intestinal Entamoeba histolytica amebiasis".)
●Bacterial causes of infectious colitis – Bacterial causes of acute diarrhea include Escherichia coli, Shigella, Salmonella, and Campylobacter. These are diagnosed via stool culture. (See "Approach to the adult with acute diarrhea in resource-rich settings".)
●Gastrointestinal parasites – Gastrointestinal parasites include Giardia, Dientamoeba fragilis, and Cryptosporidium. These can cause a prolonged watery diarrheal illness with associated malaise, nausea, anorexia, and crampy abdominal pain; they do not cause dysentery. They are diagnosed via stool microscopy. (See related topics.)
●Inflammatory bowel disease – Clinical manifestations of inflammatory bowel disease include bloody diarrhea and abdominal pain. The diagnosis is established by colonoscopy and biopsy. (See "Clinical manifestations, diagnosis, and prognosis of ulcerative colitis in adults".)
TREATMENT — The optimal approach to treatment of balantidiasis is uncertain. In general, it is reasonable to treat symptomatic patients. Data are limited regarding treatment of asymptomatic cyst excretion; we favor a course of therapy. Treatment consisting of tetracycline (500 mg orally four times daily for 10 days) is effective therapy for B. coli [20]. An alternative is metronidazole (750 mg orally three times daily for five days).
Alternative agents include other 5-nitroimidazole compounds such as tinidazole (2 g for diarrhea or 2 g for three days for colonic ulceration) and paromomycin (500 mg three times daily for 5 to 7 days), based on the efficacy of these against other protozoal infections.
Follow-up stool examination is warranted if symptoms persist.
For prevention of infection, travelers should adhere to routine precautions about consumption of food and water. (See "Travel advice", section on 'Food and water'.)
SUMMARY AND RECOMMENDATIONS
●Balantidium coli is a protozoa that can cause colitis. Human balantidiasis is most prevalent in tropical and subtropical regions. The principal means for acquisition of infection by humans consist of porcine fecal contamination of food or water. (See 'Epidemiology' above.)
●Most cases are asymptomatic; patients with debilitating conditions or other infections are at increased risk for developing symptomatic infection. Symptoms can include nausea, vomiting, weight loss, abdominal pain, and prominent diarrhea that may be bloody. Fulminant disease with intestinal perforations occurs rarely and can be a potentially fatal septic complication. (See 'Clinical manifestations' above.)
●The diagnosis of B. coli infection is established by detection of trophozoites or cysts in stool examinations or mucosal scrapings obtained at colonoscopy or sigmoidoscopy (picture 1). (See 'Diagnosis' above.)
●We suggest tetracycline for treatment of B. coli (Grade 2C); metronidazole is an alternative agent. For prevention of infection, travelers should adhere to routine precautions about consumption of food and water. (See 'Treatment' above.)
