The genus Plasmodium contains several species of obligate intracellular parasites within the class of protozoa called Sporozoa, a class that also contains two other genera of protozoa that are pathogenic for humans: Babesia and Toxoplasma. Although a large number of Plasmodium species naturally infect a variety of animals, including monkeys, rodents, birds, and reptiles, only four species infect humans: P. falciparum, P. vivax, P. malariae, and P. ovale. Each species has certain morphologic characteristics by which the parasite can be identified, and each has biologic and pathogenic features of clinical importance
