This holotrichasin, trichostomorid family was once considered to belong in the Heterotrichorida; Faure-Fremiet (1955) showed its proper position. Cilia are arranged in longitudinal rows over the whole body. The peristome forms a pouch with a triangular opening containing a short adoral zone of membranelles. There is no concretion vacuole.
The body is ovoid, ellipsoid to subcylindrical. The macronucleus is elongated. There is a single micronucleus. The contractile vacuole and cytopyge are terminal.
Many species of Balantidium have been named, based on the host in which they occur and on the size and shape of their body and macronucleus (cf. Hegner, 1934; Kudo and Meglitsch, 1938). However, many of these are probably not valid. For instance, McDonald (1922) separated B. suis from B. coli, both from swine, on the basis of its slenderer body and straighter macronucleus, but Levine (1940, 1940a) showed that Balantidium from swine changed dimensions upon cultivation, and that a single strain could resemble B. coli if it was full-fed and B. suis if it was starved. Lamy and Roux (1950) found both suis and coli forms in clone cultures started from single organisms and considered the suis forms to be conjugants and the coli forms trophozoites. Auerbach (1953) concluded from his cytological and cultural studies that the 2 forms were not different species.
Synonym: Balantidium suis.
Disease: Balantidiosis, balantidial dysentery.
Hosts: Pig, man, chimpanzee, orang-utan, rhesus monkey, cynomolgus monkey, other macaques, rarely dog and rat.
Location: Cecum, colon.
Geographic Distribution: Worldwide.
Prevalence: B. coli is extremely common in swine, having been reported in 21 to 100% of them in various surveys (Kennedy and Stewart, 1957), but the lower figures may reflect the examination technic rather than the true incidence (de Carneri, 1958). It is much less common in man, its incidence in 12 surveys comprising 24,837 fecal specimens thruout the world being 0.77% according to Belding (1952). Shookhoff (1951) found it in 0.6% of approximately 3000 Puerto Rican patients. Swartzwelder (1950) described 16 human cases in New Orleans; these represented more than 1/4 of all the available reports in the United States.
B. coli occurs in primates other than man, but is not common. Habermann and Williams (1957) found it at postmortem examination of 5 of 615 rhesus monkeys obtained by the National Institutes of Health from various importers; the animals had died of various diseases. They did not find it in 93 cynomolgus monkeys (Macaca philippinensis). Cockburn (1948) described an epidemic of enteritis among the larger primates at the London Zoo which appeared to be due to Balantidium. Benson, Fremming and Young (1955) reported it in captive chimpanzees.
Balantidium has been seen on rare occasions in the dog. Dikmans (1948) reported a case in a dog in North Carolina. Bailey and Williams (1949) reported one from Tennessee, and Hayes and Jordan (1956) reported one from Georgia.
Bogdanovich (1955) found B. coli in 6 out of 150 Norway rats in a Russian slaughter house.
"Balantidium coli" has been reported from the zebu (Cooper and Gulati, 1926) and water buffalo (Priestley, 1944), but Lubinsky (1957) considered it to be a late exconjugant of Buxtonella sulcata, which he had found commonly in the zebu. The longitudinal furrow is inconspicuous in this stage and is easily overlooked.
Morphology: The trophozoites are ovoid, with a subterminal cytostome at the smaller end, and measure 30 to 150 by 25 to 120 u. The cytopyge is near the posterior end. The macronucleus is sausage- or kidney-shaped, and the micronucleus lies near the center of 1 side. There are 2 contractile vacuoles, 1 terminal and the other near the center of the body. There are many food vacuoles containing starch grains, cell fragments, bacteria, erythrocytes, etc.; starch is the most important food. The surface is covered by slightly oblique longitudinal rows of cilia.
Krascheninnikow and Wenrich (1958) studied the morphology and division of B. coli in detail, Auerbach (1953), Sen Gupta and Ray (1955) and Lom (1955) reported on cytologic and cytochemical studies.
The cysts are spherical to ovoid and measure 40 to 60 u in diameter. They are slightly yellowish or greenish, with hyaline cytoplasm. The cyst wall is composed of 2 membranes.
Life Cycle: B. coli reproduces by transverse binary fission (Krascheninnikow and Wenrich, 1958), Conjugation also takes place (Nelson, 1934; Svensson, 1955), and resistant cysts are formed.
Pathogenesis: In the pig, Balantidium coli is ordinarily a commensal in the lumen of the large intestine, where it lives on starcn, other ingesta and bacteria. It does not seem able to penetrate the intact intestinal mucosa by itself. Enormous numbers of Balantidium may be found in the lumen of the cecum of pigs with normal cecal mucosae. However, once some other organism or condition has initiated a lesion, Balantidium may be a secondary invader and may be found deep in the ulcer. It produces hyaluronidase (Tempelis and Lysenko, 1957), which might help it to enlarge the lesions by attacking the ground substance between the cells, altho it would not help it to initiate the lesions.
Balantidium is pathogenic in man and other primates. It causes diarrhea or dysentery, and produces undermining lesions similar to those caused by Entamoeba histolytica. The protozoa may be found down to the muscularis mucosae, the ulcers are infiltrated with round cells, and coagulation necrosis and hemorrhagic areas may be present. The protozoa often occur in nests within the tissues or even in the capillaries, lymph ducts and neighboring lymph nodes. The lesions in the pig and other animals are similar. The disease in man has been reviewed by Swartzwelder (1950), Shookhoff (1951) and Arean and Koppisch (1956).
The infected dog described by Dikmans (1948) died of a severe diarrheal disease, and ulcers were found in the intestine at necropsy. In the case reported by Bailey and Williams (1949), the animal had dysentery for several days beginning several days after it ate the intestines of a hog, but it recovered.
Lesions in the ceca of some naturally infected rats were described by Bogdanovich (1955).
Bionomics and Epidemiology: Balantidium may be transmitted by ingestion of either cysts or trophozoites. The cysts are more resistant to environmental conditions, Svensson (1955) found that the trophozoites of different strains of B. coli from the pig differ in their resistance to heat and cooling. Most strains survive heating to 47° C for more than 15 minutes but survive at room temperature for less than 3 days. A cold-resistant strain survived heating for only 5 to 10 minutes, but remained alive at room temperature for 5 days or more. B. coli from man is similar to the latter. The cysts may remain alive for weeks in pig feces if they do not dry out.
The pig is the usual source of infection for man. Contact with swine has been noted in more than half the human cases reported (Arean and Koppisch, 1956), and Shookhoof (1951) obtained a history of close contact with pigs in practically all the cases he observed in Puerto Rico. Chimpanzees and other primates appear to have their own infection pool.
Diagnosis: Balantidium can be easily recognized by microscopic examination of intestinal contents or by histologic examination of intestinal lesions.
Cultivation: B. coli was first cultivated by Barret and Yarbrough (1922) in a medium consisting of 1 part inactivated serum and 16 parts of 0.5% sodium chloride solution. It has since been cultivated by many workers. Schumaker (1931) and Levine (1940) used a medium consisting of 9 parts of Ringer's solution and 1 part of horse serum plus about 0.007 g rice starch per tube containing 10 ml of the medium. Tempelis and Lysenko (1957) used an agar slant of Difco Entamoeba histolytica medium overlaid with Balamuth's egg yolk infusion plus rice starch, 500 units per ml of streptomycin and 250 units per ml of penicillin; this medium was used successfully to establish clone cultures from single microorganisms.
Treatment: No treatment is necessary in swine. Carbarsone has been used in man. Young and Burrows (1943) administered 0.25 to 0.5 g twice a day for 10 days. However, DeLanney (1943) found that carbarsone did not eliminate all the parasites and recommended 2.1 g diiodohydroxyquin (diodoquin) daily for 20 days. Swartzwelder (1950) recommended diodoquin if carbarsone failed. More recently, chlortetracycline and oxytetracycline have been found effective (Arean and Koppisch, 1956; Neghme et al., 1951).
Benson, Fremming and Young (1955) treated chimpanzees with 250 mg carbarsone daily for 10 days, concealing the drug in fruit or fruit juices.
Prevention and Control: Sanitary measures designed to prevent ingestion of cysts or feces should prevent balantidial infections.