Etiology and Epidemiology

Although A. duodenale can be ingested in contaminated food, water, or possibly breast milk, the more common route of infection, and the only one for N. americanus, is through penetration of the skin. Larvae in the soil typically enter through the skin of the feet, frequently causing dermatitis, once called "ground itch" or "dew poison" in the southern United States, and "water itch" or "coolie itch" in India. Then the parasites travel through the bloodstream to the alveoli of the lungs, climb the respiratory tree, and make their way into the esophagus. During their migration through the airways into the esophagus, the host sometimes develops a cough, wheeziness, or temporary hoarseness. The hookworms are then swallowed and pass into the gut, where some will successfully attach themselves to the small intestinal mucosa and begin nourishing themselves on their host's blood. In the small intestine, hookworms will grow to a length of about 1 centimeter and mature in 6 to 8 weeks after initial infection. Depending on the species, hookworms generally live from 1 to 5 years, although a few apparently live longer. The adult female may produce thousands of ova per day, which pass out of the body with the host's feces. Egg production varies with the species, the age of the worm, the number of worms in the gut, and the degree of the host's resistance. If deposited on warm, moist soil, the eggs will produce larvae that will molt twice over 2 weeks before becoming infective and can survive in a free-living state for over a month before finding a host.

Hookworms thrive on human ignorance and poverty. If the billions of people living in areas of hookworm infestation were able to eat moderately well, wear good shoes, and defecate in latrines, hookworm disease would soon no longer pose a serious threat to human health. Understood as an index of socioeconomic status, hookworm infection will likely remain a daunting public health problem as long as there are poor people, inadequately educated, living in warm climates. The historical record is not reassuring: Documentary and physical evidence suggest that hookworms have infected humans in different parts of the world for millennia. In the early decades of the twentieth century, massive campaigns launched to eradicate hookworm disease ended in disillusionment and failure. Modern public health officials now pursue the more modest goal of containment, with reductions in the incidence of acute infection. If anything resembling the optimism of the early days of antihookworm work still survives, it is in the possibility that a vaccine may yet be pro duced, thus permitting overmatched agencies to finesse the intractable political problems of malnutrition and poverty.

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