hookworm, any of a number of bloodsucking nematodes in the phylum Nematoda, order Strongiloidae that live as parasites in humans and other mammals and attach themselves to the host's intestines by means of hooks. Hookworm infection in humans is caused by infestation with Ancylostoma duodenale (the European species) or with Necator americanus (the American species). It is found in tropical and subtropical climates, especially where the inhabitants do not wear shoes or stockings and where the soil is contaminated by human excrement. The larva of the hookworm, living in moist soil or mud, easily penetrates the exposed skin, usually the sole of the foot, and is then carried by the blood to the lungs. An early sign of hookworm infestation is a dermatitis at the site of entry, known as ground itch. As the larva passes through the lungs, it causes episodes of coughing with bloody sputum. Raised with the mucus into the mouth, the larva is then swallowed. It may also be swallowed with polluted drinking water or with unclean vegetables eaten raw. By means of its hooks the larva attaches itself to the upper portion of the small intestine, where it nourishes itself on the blood of its host. The larva matures and the female produces eggs, as many as 30,000 per day, that are passed from the intestine with the feces, usually to contaminate the soil still further. The drain on the blood of the host results in anemia. This, together with the resulting abdominal pain and diarrhea, causes general debility. Hookworm is treated with drugs, notably tetrachloroethylene, that loosen and destroy the parasite, as well as with specifics for the anemia and abdominal symptoms. Incidence of this disease, which was once seriously prevalent, has been much reduced by improved sanitation and the wearing of shoes.