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The Merck Manual--Second Home Edition logo
 
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Chapter 196. Parasitic Infections
Topics: Introduction | Amebiasis | Ascariasis | Babesiosis | Cryptosporidiosis | Giardiasis | Hookworm Infection | Malaria | Pinworm Infection | Schistosomiasis | Tapeworm Infection | Toxocariasis | Toxoplasmosis | Trichinosis | Whipworm Infection
 
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Hookworm Infection

Hookworm infection (ancylostomiasis) is a disease of the intestines, resulting in anemia and occasionally skin rash, respiratory problems, or abdominal pain.

About 1 billion people are infected with hookworms, which are intestinal roundworms. The infection is most common in warm, moist places where sanitation is poor. Two species of hookworm cause infection in people: Ancylostoma duodenale, which is present in India, China, Japan, and the Mediterranean area; and Necator americanus, which is present in the tropical areas of Africa, Asia, and the Americas. Necator americanus also occasionally causes infection in the southern part of the United States.

click here to view the figure See the figure Life Cycle of the Hookworm.

Eggs are passed in stool and hatch in the soil after incubating for 1 to 2 days. Larvae emerge to live in the soil. When fully developed, the larvae can penetrate the skin. A person can become infected by walking barefoot or sitting in contaminated soil. Once they enter the body, the larvae move through the lymphatic vessels and the bloodstream to the lungs. The larvae pass into the air spaces, climb the respiratory tract into the throat, and are swallowed. About a week after penetrating the skin, they reach the intestine. Once inside the intestine, the larvae develop to adults, attach themselves by their mouths to the lining of the upper small intestine, produce substances that keep blood from clotting, and live on blood from the wall of the host's intestine.

Symptoms and Diagnosis

An itchy, red, raised rash (ground itch) may develop where the larvae penetrated the skin. The migration of the larvae through the lungs can cause fever, coughing, and wheezing. Adult worms can cause pain in the upper abdomen when they first attach in the intestine. Over time, anemia develops as blood is lost and the person becomes iron deficient. In children, slow growth, heart failure, and widespread tissue swelling may develop when the resulting anemia is severe.

The diagnosis is made by identifying hookworm eggs in a sample of stool. If the stool is not examined for several hours, the eggs may hatch and release larvae.

Treatment

A doctor prescribes an oral drug, such as albendazole, mebendazole, or pyrantel pamoate. Because of possible adverse effects to the fetus, these drugs cannot be taken by pregnant women. Iron supplements are given to people with anemia.

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