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.

Cause

Hookworm infection is a disease caused by several species of parasites. The symptoms of animal hookworm infection in people depend on how people get the infection. Early stages of animal hookworms, the larvae, can infect people and travel through different parts of the human body. This is called larva migrans (LAR-va MIGH-granz). People can also get painful and itchy skin infections when animal hookworm larvae move through their skin. If a person accidentally eats animal hookworm eggs, then the larvae that hatch out of the eggs can reach the intestine and cause bleeding, inflammation (swelling), and abdominal pain.

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.

Risks

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.

Symptoms

Itching and a rash at the site of where skin touched soil or sand is usually the first sign of infection. These symptoms occur when the larvae penetrate the skin. While a light infection may cause no symptoms, heavy infection can cause anemia, abdominal pain, diarrhea, loss of appetite, and weight loss. Heavy, chronic infections can cause stunted growth and mental development.

Can a hookworm infection cause any serious health problems?

Yes. The most serious results of hookworm infection are the development of anemia and protein deficiency caused by blood loss. When children are continuously infected by many worms, the loss of iron and protein can retard growth and mental development, sometimes irreversibly. Hookworm infection can also cause tiredness, difficulty breathing, enlargement of the heart, and irregular heartbeat. Sometimes hookworm infection is fatal, especially among infants.

What should I do if I think I have a hookworm infection?

Visit your health care provider. Infection is diagnosed by identifying hookworm eggs in a stool sample.

Treatment

In countries where hookworm is common and reinfection is likely, light infections are often not treated. In the United States, hookworm infections are generally treated for 1-3 days with medication prescribed by your health care provider. The drugs are effective and appear to have few side effects. For children under the age of 2, the decision to treat should be made by their health care provider.

Another stool exam should be repeated 1 to 2 weeks after therapy. If the infection is still present, treatment will be given again. Iron supplements will be ordered if you have anemia.

Prevention

Do not walk barefoot or contact the soil with bare hands in areas where hookworm is common or there is likely to be feces in the soil or sand.

References

Bundy DAP. Is the hookworm just another geohelminth? In: Hookworm Disease, Schad GA, Warren KS, eds. London and Philadelphia: Taylor and Francis1990;147-64.

Hotez PJ, Pritchard DI. Hookworm infection. Scientific American 1995;June:68-74.

Roche M, Layrisse M. The nature and causes of "hookworm anemia." Am J Trop Med Hyg 1966:15;1030-1100.

Schad GA, Warren KS. Hookworm disease: current status and new directions. London: Taylor and Francis, 1990.