Hookworm is an intestinal parasite of humans that usually causes mild diarrhea or cramps.
Heavy infection with hookworm can create serious health problems for newborns, children, pregnant women, and persons who are malnourished. Hookworm infections occur mostly in tropical and subtropical climates and are estimated to infect about 1 billion people -- about one-fifth of the world's population.
One of the most common species, Ancylostoma duodenale, is found in southern Europe, northern Africa, northern Asia, and parts of South America. A second species, Necator americanus was widespread in the southeastern United States early in this century.
The Rockefeller Sanitary Commission was founded in response, and hookworm infection has been largely controlled.