Definition: Single-celled eukaryotes (organisms that possess membrane-bound organelles and nuclei).
Protozoa are found as ubiquitous free-living organisms in the environment. They are classified as sporozoa (intracellular parasites), flagellates (which possess tail-like structures for movement), amoeba (which move using temporary cell body projections called pseudopods), and ciliates (which move by beating multiple hair-like structures called cilia).
Infections caused by protozoa can be spread through ingestion of cysts (the dormant life stage), sexual transmission, or through insect vectors. Common infectious diseases caused by protozoans include malaria, giardia and toxoplasmosis.
