Hookworm Disease

One of the most common roundworm infections is hookworm. Like ascarids, hookworms are picked up as a result of unsanitary conditions. Hookworm eggs are passed in human feces onto the ground where they develop into infective larvae. When the soil is cool, the worms crawl to the nearest moist area and extend their bodies into the air. They remain there – waving their bodies to and fro – until they come into contact with the skin of a suitable host or until they are driven back down by the heat.

Hookworm is endemic in those tropical and subtropical countries in which people defecate on the ground and soil moisture is most favorable. Necator americanus is the prevailing species in the southeastern United States.

The infection is usually contracted by persons walking barefoot over contaminated soil. In penetrating the skin, the larvae may cause an allergic reaction. It is from the itchy patch at the site of entry that the early infection gets its nickname "ground itch." Once larvae have broken through the skin, they enter the bloodstream and are carried to the lungs. (Unlike ascarids, however, hookworms do not usually cause pneumonia.) The larvae migrate from the lungs up the windpipe to be swallowed and carried back down to the intestine.

Maturation of the worms in the intestine before eggs appear in the stool is sometimes marked by the onset of diarrhea, particularly in a previously uninfected person. Other signs and symptoms at this stage include vague abdominal pain, intestinal cramps, colic, and nausea.

Scientists have learned that persons in good health and on a diet containing adequate iron can tolerate the presence of these worms in small or moderate numbers with no ill effects. In chronic infections, if the number of parasites become great enough, serious anemia can occur as a result of blood loss from the worms attaching themselves to the intestine and sucking the blood and tissue juices of the host.

To diagnose hookworm, the doctor will examine stool specimens to look for and count the number of eggs. If the egg output is large enough – more than 2,000 eggs per gram of stool – the doctor will assume that the infection may cause anemia and start treating the patient.

If humans come into contact with larvae of the dog hookworm or the cat hookworm, or of certain other hookworms that do not infect humans, the larvae may penetrate the skin. But the larvae are unable to complete their migratory cycle in humans. Instead, the larvae move just below the skin producing snake-like markings. This is referred to as a creeping eruption or cutaneous larva migrans.

Ancylostoma canium, an illness caused by a particular species of dog hookworm, has been described in Australia. This worm may almost complete its development in the lower small intestine, but produces a severe inflammatory reaction in the bowel, causing abdominal pain, diarrhea, and an increase in peripheral blood eosinophils.

Once diagnosed with hookworm, the patient can be treated effectively with drugs such as mebendazole. Frequently, the doctor will supplement the drug therapy with dietary iron.

National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH) Bethesda, MD 20892, October 1998.