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Hookworm is a roundworm infestation affecting the small intestine and lungs. The worms are about 1/2 inch long.

Causes, incidence, and risk factors

The disorder is caused by infestation with the roundworms Necator americanus, Ancylostoma duodenale, Ancylostoma ceylanicum, or Ancylostoma braziliense. The first 2 occur in humans only. The last 2 types also occur in animals.

Hookworm disease is widespread in the moist tropics and subtropics, and it affects over 1 billion people worldwide. In developing nations, the disease indirectly causes the death of many children by increasing their susceptibility to other infections that could normally be tolerated.

There is very little risk of contracting the disease in the U.S. because of advances in sanitation and control of wastes.

The larvae (immature form of the worm) penetrate the skin, where an itchy rash called ground itch may develop. The larvae migrate to the lungs via the bloodstream, enter the airways and cause coughing.

After traveling up the bronchi, the larva are swallowed. When the larvae are swallowed, they infect the small intestine and develop into adult worms. Adult worms and larvae are excreted in the feces.

Most people have no symptoms once the worms enter the intestines. However, iron deficiency anemia caused by loss of blood may result from heavy infestation.


Note: There are often no symptoms.

Signs and tests


The objective of treatment is to cure the infestation, to treat complications of anemia, and to improve nutrition. Parasite-killing medications such as mebendazole or albendazole are usually prescribed. Ivermectin, used for other worm infections, is not effective for hookworm.

Symptoms and complications of anemia are treated as they arise. There is often a recommendation made to increase the amount of protein in the diet to improve nutrition.

Expectations (prognosis)

Complete recovery occurs if treatment is given before serious complications develop. The infection is easily eradicated with treatment.


  • Anemia
  • Severe protein loss with ascites

Calling your health care provider

Call for an appointment with your health care provider if symptoms of hookworm infection develop.


Improvement in sanitation measures in developing countries is necessary for prevention of infection.


Kucik CJ, Martin GL, Sortor BV. Common intestinal parasites. Am Fam Physician. 2004 Mar 1;69(5):1161-8.

Beers MH, Berkow, R. eds. Parasitic Infections. In: The Merck Manual of Diagnosis and Therapy. Sec. 13. Ch. 161. Merck & Co, Inc: 1999-2005.


Hookworm - mouth of the organism
Hookworm - mouth of the organism
Hookworm - close-up of the organism
Hookworm - close-up of the organism
Hookworm - Ancyclostoma caninum
Hookworm - Ancyclostoma caninum
Hookworm egg
Hookworm egg
Hookworm rhabditiform larva
Hookworm rhabditiform larva
Digestive system organs
Digestive system organs

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