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Protozoa
(pro″to-zo´ә)
a subkingdom (formerly a phylum) comprising the unicellular eukaryotic organisms; most are free-living, but some lead commensalistic, mutualistic, or parasitic existences. Newer classifications have subdivided the Protozoa into a number of smaller phyla. Pathogenic protozoa include
species of Plasmodium, the cause of human malaria; Trypanosoma gambiense, the cause of African trypanosomiasis; Toxoplasma gondii, of which house cats are the reservoir and humans the intermediate host; Entamoeba histolytica, the cause of amebic dysentery; and Balantidium coli and Isospora belli, both of which cause diarrhea in humans. Protozoa are passed by ingestion of food contaminated with infected feces; this can be prevented by handwashing
and stool precautions.

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