Balantidium coli
This is a common ciliate parasite of man, lower primates and hogs. Pathogenesis is similar to that seen in E. histolytica intestinal infections. Extra-intestinal involvement is rare.
Both a trophozoite ( below left) and a cyst stage (middle) are known. It is most common in tropical regions of the world with an infection rate of about 1% in humans and from 20 to 100% in pigs. Human infections are most common where malnutrition occurs, where pigs share habitation with humans, and where fecal contamination of food and water can occur. The parasite appears to be nonpathogenic in pigs. Stained preparations and histologic preparations clearly show the large kidney-shaped macronucleus (right). Also present is a spherical micronucleus, two contractile vacuoles (unique among parasitic protozoan parasites), and food vacuoles. Asexual reproduction is by transverse fission although conjugation also occurs. Results of human infection range from asymptomatic to severe with invasion of the mucosal lining followed by hemorrhage and ulceration occurring. Most human cases disappear spontaneously, while some become asymptomatic, resulting in a carrier state. Treatment usually involves oxytetracycline therapy, usually lasting for 10 days. Many commensial and free-living ciliates are also known from ruminants and horses as well as free-living aquatic species and should be differentiated from B. coli.
In most situations, B. coli is harmless to pigs and man although diarrhea and dysentery are known. Disease, when it would occur, would be clinically indistinguishable from other causes of hemorrhagic colitis.
Ichthyophthirus multifillis- Agent of "ich".
This is a ciliate parasite infecting fish. It is common in both outdoor aquaculture operations and indoor hobby tanks. The life cycle is complicated with both free-swimming and encysted stages. Water temperature is an important factor in the life cycle of this parasite. The stage that causes pathogenesis on fish (tomonts) appear as white dots on the gills, fins and body of the fish (below).
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