Medical Definition of balantidium
1 capitalized : a genus of large parasitic ciliate protozoans (order Heterotricha) including one (B. coli) that infests the intestines of some mammals and especially swine and may cause a chronic ulcerative dysentery in humans
2plural bal·an·tid·ia \-ē-ə\play : a protozoan of the genus Balantidium
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