Humans are hosts to nearly 300 species of parasitic worms and over 70 species of protozoa,
some derived from our primate ancestors and some acquired from the animals we have
domesticated or come in contact with during our relatively short history on Earth.
Our knowledge of parasitic infections extends into antiquity, and descriptions of
parasites and parasitic infections are found in the earliest writings and have been
confirmed by the finding of parasites in archaeological material. The systematic study
of parasites began with the rejection of the theory of spontaneous generation and
the promulgation of the germ theory. Thereafter, the history of human parasitology
proceeded along two lines, the discovery of a parasite and its subsequent association
with disease and the recognition of a disease and the subsequent discovery that it
was caused by a parasite. This review is concerned with the major helminth and protozoan
infections of humans: ascariasis, trichinosis, strongyloidiasis, dracunculiasis, lymphatic
filariasis, loasis, onchocerciasis, schistosomiasis, cestodiasis, paragonimiasis,
clonorchiasis, opisthorchiasis, amoebiasis, giardiasis, African trypanosomiasis, South
American trypanosomiasis, leishmaniasis, malaria, toxoplasmosis, cryptosporidiosis,
cyclosporiasis, and microsporidiosis.