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Hookworm infection remains a major health burden in developing countries.1 As many as 740 million people in the world are infected with Ancylostoma duodenale, Necator americanus, or both.2 Infections with A duodenale occur in focal regions of Africa, Asia, and South America, whereas N americanus is the predominant hookworm worldwide, with the greatest number of infections in North and South America, equatorial Africa, much of Southeast Asia, and some Pacific islands. It is important to recognize that there is significant overlap in the geographic pattern of infection and that mixed infections occur frequently. Although common in southern states in the early part of the 20th century, today there is little evidence of hookworm transmission in the United States. Other species that occasionally cause intestinal disease in humans include Ancylostoma ceylanicum, found in India and Southeast Asia,3 and the dog hookworm Ancylostoma caninum, which has been associated with eosinophilic enteritis in Australia.4 Zoonotic infection with Ancylostoma braziliense causes cutaneous larva migrans.5


Populations at highest risk for significant disease sequelae include preschool and school-age children, adolescents, and women of childbearing age, although adults who work in agricultural occupations are also at risk for high-intensity infection. Vulnerable populations such as young children and pregnant or lactating women are at greater risk of anemia due to relatively high iron requirements.6 Unlike Ascaris lumbricoides and Trichuris trichiura, the intensity of hookworm infection appears to increase with age, defining the elderly as another high-risk group for severe disease.7


The hookworm life cycle begins with the excretion of fertilized eggs within the feces of an infected individual. The eggs hatch to release first-stage (L1) larvae, which undergo two subsequent molts to the infective third stage (L3). These L3 hookworm larvae migrate along moisture and temperature gradients within the soil until they encounter a permissive host. When larvae contact the skin, they quickly penetrate the epidermis and dermis, ultimately invading small blood vessels and entering the venous circulation. They are then carried passively to the heart and lungs, where they lodge in the pulmonary capillaries and break through to the alveolar space. Larvae then migrate up the respiratory tree, are swallowed, and undergo their final developmental molts to the adult stage when they reach the small intestine. Once in the proximal small bowel, the adult worms attach to the mucosal surface and begin to feed (Fig. 329-1 and eFig. 329.1). Adult hookworms secrete anticoagulants, platelet inhibitors, and hemoglobin-degrading proteases that facilitate blood feeding and digestion of red blood cells.8-10 When the plug of intestinal mucosa at the site of attachment has been digested, the worm releases and reattaches at a new site. Male and female worms mate, and the female releases 10,000 to 30,000 eggs per day into the intestinal lumen. It takes approximately 6 weeks for eggs to appear in the feces of an infected individual.


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