Protozoan infections are parasitic diseases caused by organisms formerly classified in the Kingdom Protozoa.[1] They include organisms classified in Amoebozoa, Excavata, and Chromalveolata.
Examples include Entamoeba histolytica, Plasmodium (some of which cause malaria), and Giardia lamblia.[2] Trypanosoma brucei, transmitted by the tsetse fly and the cause of African sleeping sickness, is another example.
The species traditionally collectively termed "protozoa" are not closely related to each other, and have only superficial similarities (eukaryotic, unicellular, motile, though with exceptions). The terms "protozoa" (and protist) are usually discouraged in the modern biosciences. However, this terminology is still encountered in medicine. This is partially because of the conservative character of medical classification, and partially due to the necessity of making identifications of organisms based upon appearances and not upon DNA.
Protozoan infections in animals may be caused by organisms in the sub-class Coccidia (disease: Coccidiosis) and species in the genus Besnoitia (disease: Besnoitiosis).
Several pathogenic protozoans appear to be capable of sexual processes involving meiosis (or at least a modified form of meiosis). Included among these protozoans are Plasmodium falciparum (malaria), Toxoplasma gondii (toxoplasmosis), Leishmania species (leishmaniases), Trypanosoma brucei (African sleeping sickness), Trypanosoma cruzi (Chagas disease) and Giardia intestinalis (giardiasis)