What is hookworm?

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.

Where are hookworms commonly found?

One of the most common species, Ancylostoma duodenale (an-cy-CLO-sto-ma doe-AH-den-al), is found in southern Europe, northern Africa, northern Asia, and parts of South America. A second species, Necator americanus (ne-KAY-tor am-er-i-CON-us), 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.

How do I get a hookworm infection?

You can become infected by direct contact with contaminated soil, generally through walking barefoot, or accidentally swallowing contaminated soil.

Hookworms have a complex life cycle that begins and ends in the small intestine. Hookworm eggs require warm, moist, shaded soil to hatch into larvae. These barely visible larvae penetrate the skin (often through bare feet), are carried to the lungs, go through the respiratory tract to the mouth, are swallowed, and eventually reach the small intestine. This journey takes about a week. In the small intestine, the larvae develop into half-inch-long worms, attach themselves to the intestinal wall, and suck blood. The adult worms produce thousands of eggs. These eggs are passed in the feces (stool). If the eggs contaminate soil and conditions are right, they will hatch, molt, and develop into infective larvae again after 5 to 10 days.

Who is at risk?

People who have direct contact with soil that contains human feces in areas where hookworm is common are at high risk of infection. Children --because they play in dirt and often go barefoot-- are at high risk. Since transmission of hookworm infection requires development of the larvae in soil, hookworm cannot be spread person to person. Contact among children in institutional or child care settings should not increase the risk of infection.