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Hookworm Infection

(Ancylostomiasis)

By Richard D. Pearson, MD, Professor of Medicine and Pathology, Associate Dean for Student Affairs, 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.

The estimated prevalence of hookworm infection is 576 to 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.

Pathophysiology

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 or otherwise come into direct contact with 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.

Zoonotic (animal) hookworm infections

Zoonotic hookworms infections include

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

Cutaneous larva migrans can occur when animal hookworms infect humans. It is caused by the larvae as they migrate through the skin and is characterized by itchy, erythematous, serpiginous skin lesions.

Diagnosis

  • Microscopic examination of stool

A. duodenale and N. americanus produce thin-shelled oval eggs that are readily detected in fresh stool. Concentration procedures are needed to diagnose light infections. 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.

Diagnosis of cutaneous larva migrans is based on the clinical manifestations. Ova are not present in the stool.

Treatment

  • Albendazole, mebendazole, or pyrantel pamoate

One of the following drugs may be used:

  • Albendazole 400 mg po as a single dose

  • Mebendazole 100 mg po bid for 3 days or 500 mg as a single dose

  • Pyrantel pamoate 11 mg/kg (maximum dose of 1 g) po once/day for 3 days

These drugs should only be used during pregnancy if benefits outweigh risks. Ivermectin is not effective.

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

Cutaneous larva migrans is a self-limited infection, but symptoms can last 5 to 6 wk. Treatment with albendazole 400 mg once/day po for 3 or 7 days or ivermectin 200 mcg/kg as a single dose is curative.

Prevention

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.

Risk of developing cutaneous larva migrans can be reduced by the following:

  • Avoiding direct skin contact with potentially infested beach sand or other soil

  • Treating cats and dogs for hookworm

Key Points

  • Hookworm larvae penetrate the skin when people walk barefoot on or otherwise come into direct contact with infested soil.

  • In humans, larvae of the hookworms Ancylostoma duodenale or Necator americanus 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, mebendazole, or pyrantel pamoate.

Resources In This Article

Drugs Mentioned In This Article

  • Drug Name
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  • ALBENZA
  • No US brand name
  • STROMECTOL

* This is the Professional Version. *