Balantidiasis (also known as balantidiosis) is defined as large-intestinal infection with Balantidium coli, which is a ciliated protozoan (and the largest protozoan that infects humans). B coli is known to parasitize the colon, and pigs may be its primary reservoir. See the image below.
See Common Intestinal Parasites, a Critical Images slideshow, to help make an accurate diagnosis.
B coli exists as a trophozoite and a cyst and usually affects the large intestine, from the caecum to the rectum. The trophozoites replicate by binary fission and conjugation, and they subsist on bacteria. Humans ingest infective cysts, which then migrate to the large intestine, cecum, and terminal ileum. The organisms primarily dwell in the lumen but can also penetrate the mucosa and cause ulcers. B coli produces hyaluronidase, potentially enhancing its ability to invade the mucosa. 
Balantidiasis is found worldwide and has an overall estimated prevalence of 1%. Balantidiasis epidemics have occurred in psychiatric hospitals in the United States.
Balantidiasis tends to be more common among persons who handle pigs. The disease is reported most commonly in Latin America; Southeast Asia; and Papua, New Guinea. In 1971, a balantidiasis outbreak involving 100 people occurred in Truk following a typhoon.  In France, a pork butcher with immunosuppression due to alcohol use developed occupational balantidiasis. 
Most cases of balantidiasis in immunocompetent individuals are asymptomatic. Mortality rates associated with acute and fulminating types of balantidiasis were as high as 30% in untreated patients prior to the introduction of antibiotics. Pneumonia has been described in patients with cancer-related immunosuppression  and has not always been associated with direct contact with pigs.
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