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Hookworm Infection


By Richard D. Pearson, MD, University of Virginia School of Medicine

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Ancylostomiasis is infection with the hookworm Ancylostoma duodenale or Necator americanus. Symptoms include rash at the site of larval entry and sometimes abdominal pain or other GI symptoms during early infection. Later, iron deficiency may develop because of chronic blood loss. Hookworms are a major cause of iron deficiency anemia in endemic regions. Diagnosis is by finding eggs in stool. Treatment is with albendazole or mebendazole.


Both hookworm species have similar life cycles. Eggs passed in the stool hatch in 1 to 2 days (if they are deposited in a warm, moist place on loose soil) and release rhabditiform larvae, which molt once to become slender filariform larvae in 5 to 10 days. The larvae can survive 3 to 4 wk if environmental conditions are favorable. Filariform larvae penetrate human skin when people walk barefoot on infested soil. The larvae reach the lungs via blood vessels, penetrate into pulmonary alveoli, ascend the bronchial tree to the epiglottis, and are swallowed. The larvae develop into adults in the small bowel; there, they attach to the wall, feeding on blood. Adult worms may live 2 yr.

Chronic blood loss leads to iron deficiency anemia. Development of anemia depends on worm burden and the amount of absorbable iron in the diet.


The estimated prevalence of hookworm infection is about 740 million, mostly in developing areas. Both A. duodenale and N. americanus occur in Africa, Asia, and the Americas. Only A. duodenale occurs in the Middle East, North Africa, and southern Europe. N. americanus predominates in the Americas and Australia; it was once widely distributed in the southern US and is still endemic on islands of the Caribbean and in Central and South America.

Other hookworms

A. braziliense and A. caninum are hookworms that have cats and dogs as the primary hosts. These hookworms cannot complete their life cycle in humans. If their larvae penetrate human skin, they typically wander in the skin, causing cutaneous larva migrans (see Cutaneous Larva Migrans), rather than migrate to the intestine.

Rarely, A. caninum larvae migrate to the intestine, where they may cause eosinophilic enterocolitis. However, they do not cause significant blood loss and anemia, and because they do not mature to full adulthood, they do not lay eggs (making diagnosis difficult). Such intestinal infection may be asymptomatic or cause acute abdominal pain and eosinophilia.

Symptoms and Signs

Hookworm infection is often asymptomatic. However, a pruritic papulovesicular rash (ground itch, cutaneous larva migrans) may develop at the site of larval penetration, usually on the feet. Migration of large numbers of larvae through the lungs occasionally causes Löffler syndrome, with cough, wheezing, eosinophilia, and sometimes hemoptysis. During the acute phase, adult worms in the intestine may cause colicky epigastric pain, anorexia, flatulence, diarrhea, and weight loss.

Chronic infection can lead to iron deficiency anemia, causing pallor, dyspnea, weakness, tachycardia, lassitude, and peripheral edema. A low-grade eosinophilia is often present. Chronic blood loss may lead to severe anemia, heart failure, and anasarca and, in pregnant women, to growth retardation in the fetus.


  • Microscopic examination of stool

A. duodenale and N. americanus produce thin-shelled oval eggs that are readily detected in fresh stool. If the stool is not kept cold and examined within several hours, the eggs may hatch and release larvae that may be confused with those of Strongyloides stercoralis. Nutritional status, anemia, and iron stores should be evaluated.


  • Albendazole or mebendazole

Albendazole 400 mg po as a single dose or mebendazole 100 mg po bid for 3 days or 500 mg as a single dose is given. These drugs should not be used during pregnancy. Ivermectin is not effective.

General support and correction of iron deficiency anemia are needed if infection is heavy.


Preventing unhygienic defecation and avoiding direct skin contact with the soil (eg, wearing shoes, using barriers when seated on the ground) are effective in preventing infection but difficult to implement in many endemic areas. Periodic mass treatment of susceptible populations at 3- to 4-mo intervals has been used in high-risk areas.

Hookworm treatment for cats and dogs is the primary means for preventing cutaneous larva migrans.

Key Points

  • Hookworm larvae penetrate human skin when people walk barefoot on infested soil.

  • Larvae travel through the bloodstream to the lungs, penetrate the alveoli, ascend to the epiglottis, are swallowed, and then mature in the intestines.

  • Infection may be asymptomatic, but a pruritic rash may appear at the site of larval penetration, and pulmonary involvement may cause cough and wheezing.

  • Intestinal involvement may cause iron deficiency anemia.

  • Diagnose by microscopic examination of stool.

  • Treat with albendazole or mebendazole.

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