Hookworm infection in humans is caused by an infection with the helminth nematode parasites Necator americanus and Ancylostoma duodenale and is transmitted through contact with contaminated soil. It is one of the most common chronic infections, with an estimated 740 million cases in areas of rural poverty in the tropics and subtropics.1 Because hookworm infection occurs predominantly among the world's most impoverished people,  it holds a unique place in modern history. For example, the reputation of pre-1949 China as the "sick man of Asia" was partly a result of the high prevalence and intensity of infection with hookworm. Mohandas Gandhi had hookworm infection in the last years of his life.  Hookworm was also a contributing factor in the slowing of economic development during the early part of the 20th century in the southern United States. Today, hookworm infection is among the most important tropical diseases in humans; the use of disability-adjusted life years as a quantitative measure of the burden of disease reveals that this infection outranks African trypanosomiasis, dengue, Chagas' disease, schistosomiasis, and leprosy. 

The greatest number of hookworm cases occur in Asia, followed by sub-Saharan Africa.  In China alone, approximately 190 million people are infected, an estimate based on a nationwide study involving the examination of fecal specimens obtained from almost 1.5 million people between 1988 and 1992.  N. americanus is the most common hookworm worldwide, whereas A. duodenale is more geographically restricted. In contrast to these major anthropophilic species, three species of zoonotic hookworm are minor causes of disease in humans. A. ceylanicum infects dogs and cats and can also infect humans but is not considered an important pathogen. The dog hookworm A. caninum causes human eosinophilic enteritis in northeastern Australia,6 and A. braziliense causes cutaneous larva migrans.