Balantidium coli

Name

Greek: balantion = small sack; kolon = terminal portion of intestine.

Geographic Distribution

Worldwide, mainly in porcines, rarely also in humans (less than 1,000 proven cases per year).

Biology/Morphology

B. coli reach a size of 50–150 μm and live in the caeca and in the colon of their hosts. This parasite belongs to the trichosomastid ciliates (Ciliophora) and is characterized by an anterior vestibulum, a cytostome-cytopharyngeal complex, several contractile vacuoles, a small/spherical micronucleus, a large macronucleus, and the lack of typical mitochondria. The surface is covered by typical cilia in regular rows which allow a significant mobility in the intestinal fluid. Reproduction occurs by binary cross-directed division, while sexual processes are involved during the rarely seen so-called conjugation, during which wandering nuclei are exchanged via a cytoplasmic bridge being formed for a short time between two trophozoites. It was noted that some trophozoites may enter the intestinal wall. Transmission of this parasite occurs by oral uptake of cysts, the wall of which is excreted by trophozoites, which then reduce their cilia (Figs. 1, 2, 3, and 4). These cysts reach a size of 50–70 μm.

Balantidium coli, Fig. 1

Life cycle of Balantidium coli in the cecum and colon of humans, pigs, rodents, and many mammals. 1 Cysts of 40–60 μm diameter are excreted with the feces. The macronucleus of this species is sausage shaped. 2 Cysts are orally ingested with food by the new host. In the intestine, the trophozoites hatch from the cysts and grow to a size of 150 × 100 μm. 2.1 The trophozoite is reproduced by repeated transverse binary fissions. Conjugation has been observed, but may occur only rarely in man. In mammals, the trophozoites may initiate lesions and ulcers of the intestine. 3 Encystment is initiated by dehydration of feces as they pass posteriad in the rectum. Trophozoites may also encyst after being passed in feces. CIcilia, CW cyst wall, CY cytopharynx, MA macronucleus, MImicronucleus (for other species of Ciliophora see Ciliophora/Table 1)

Balantidium coli, Fig. 2

Light micrograph of B. coli prior to entering the intestinal wall

Balantidium coli, Fig. 3

B. coli stage inside the intestinal wall in division

Balantidium coli, Fig. 4

B. coli cyst stage inside the intestinal fluid

Symptoms of Disease

Man (balantidiasis)

Mainly, humans working in pig elevation or in slaughter houses are infected. In most cases symptoms of disease do not appear. However, in cases of a predisposition or any immunosuppression, symptoms of disease may occur after an incubation period of about 4 days. As in bacteria-derived intestinal diseases, spastic slimy diarrheas may occur 8–12 times per day. In cases of peritonitis even bloody stools may occur. Due to the huge loss of water, infected persons may suffer from dizziness and nausea. Due to higher rates of parasites that had entered the peritoneum (rare) cases of death had been reported.

Animals (balantidosis)

Pigs mainly suffer from heavy and numerous watery-slimy diarrheas leading to typhlitis and colitis. Due to high loss of intestinal fluids the animals show considerable loss of weight and weakness. Young pigs are in general only rarely infected, while pigs over 4 weeks show infection rates up to 100 %. This is a sign that B. coli is only a facultative agent of disease. Heavily infected animals, however, show numerous hemorrhagies in the colon and even in the stomach.

Diagnosis

Microscopic determination of cysts by fecal standard techniques such as M.I.F., S.A.F., or flotation.

Infection Route

Oral uptake of cysts from pig feces (farmers, butchers, other farmed pigs, etc.).

Prophylaxis

Avoid contact with human or pig feces.

Incubation Period

Days up to weeks.

Prepatent Period

Four to seven days.

Patent Period

Eventually, years in nonsymptomatic infections.

Treatment

• (a) Pigs: no safe medical cure available; symptomatically: tetracyclines or trimethoprim plus sulfonamids

• (b) Humans: Metronidazole (3 × 750 mg/day for adults; 35–50 mg/kg bodyweight for children) divided in three dosages per day for 5 days or tetracyclines (4 × 500 mg/day) for 10 days