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Ancylostomiasis
is infection with 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. Hookworms are
a major cause of iron deficiency anemia in endemic regions. Diagnosis
is by finding eggs in stool. Treatment is albendazole, mebendazole,
or pyrantel pamoate.
Etiology
and 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. Filariform larvae penetrate human skin, reach the lungs via blood vessels, penetrate into pulmonary alveoli, ascend the respiratory tree to the epiglottis, and are swallowed. The larvae develop into adults that attach to the wall of the small bowel, feeding on blood. Chronic blood loss leads to iron deficiency anemia. The development of anemia depends on worm burden and the amount of absorbable iron in the diet. Adult worms may live ≥ 2 yr.
The estimated prevalence of hookworm infection is about 1 billion, mostly in tropical latitudes. Both A. duodenale and N. americanus are found in Africa, Asia, and the Americas. Only A. duodenale is found 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. It is still endemic on islands of the Caribbean and in Central and South America.
Infection with A. caninum, which ordinarily infects dogs, is a common cause of eosinophilic enteritis in Queensland, Australia. Several cases have been diagnosed in the US. Eggs of A. caninum are not usually found in human stool. 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—see Parasitic Skin Infections: Cutaneous Larva Migrans) may develop at the site of larval penetration. Migration of large numbers of larvae though the lungs occasionally causes Löffler's pneumonia, with cough, wheezing, 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 and hypoproteinemia, causing pallor, dyspnea, weakness, tachycardia, lassitude, and peripheral edema. A low-grade eosinophilia is often present. Chronic blood loss may lead to severe anemia, growth retardation, heart failure, and anasarca.
Diagnosis,
Treatment, and Prevention
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 (a single dose of 400 mg po) or mebendazole (100 mg po bid for 3 days) is given. Cure rates are > 99%. Pyrantel pamoate (11 mg/kg po once/day [1 g maximum] for 3 days) is also effective. These drugs should not be used in pregnancy. 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 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.
Last full review/revision November 2005
Content last modified November 2005
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