Hookworm: An intestinal parasite that usually causes diarrhea or cramps. Heavy infestation with hookworm can be serious for newborns, children, pregnant women, and persons who are malnourished. Hookworm infections occur mainly in tropical and subtropical climates and affect about 1 billion people -- about one-fifth of the world's population. One of the most common species of hookworm, Ancylostoma duodenale, is found in southern Europe, northern Africa, northern Asia, and parts of South America. A second species, Necator americanus, was once widespread in the southeastern US early in the 20th century.
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.
Hookworm infection is contracted from contact with soil contaminated by hookworm, by walking barefoot or accidentally swallowing contaminated soil. 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.
Chronic heavy hookworm infection can damage the growth and development of children. The loss of iron and protein retards growth and mental development, sometimes irreversibly. The first signs of hookworm infection are itching and a rash at the site where the larvae penetrate the skin. These signs may be followed by abdominal pain, diarrhea, loss of appetite and weight loss, and anemia. Hookworm can also cause difficulty breathing, enlargement of the heart, and irregular heartbeat. Hookworm infection have been known to be fatal, particularly in infants.
The diagnosis is by identifying hookworm eggs in a stool sample. In countries where hookworm is common and reinfection is likely, light infections are often not treated. In the US, hookworm infections are generally treated for 1-3 days. The drugs are effective and appear to have few side effects. Another stool exam should be repeated 1 to 2 weeks after therapy. If the infection is still present, treatment is repeated. Iron supplements are in order with anemia.
People infected with hookworm are half as likely to have asthma as those without it, in keeping with the hygiene hypothesis of asthma -- the theory that because of better hygiene, people today tend to get fewer infections so they are at greater risk of allergic conditions such as asthma.
To prevent hookworm, do not walk barefoot or contact the soil with bare hands in areas where hookworm is common or there are likely to be feces in the soil or sand.