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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Intestinal Nematodes

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HookWorm Disease

Hookworm infection is found worldwide between the latitudes of 45°N and 30°S. Trans-mission requires deposition of egg-containing feces on shady, well-drained soil;

HOOK WORM DISEASE

EPIDEMIOLOGY

Hookworm infection is found worldwide between the latitudes of 45°N and 30°S. Trans-mission requires deposition of egg-containing feces on shady, well-drained soil; develop-ment of larvae under conditions of abundant rainfall and high temperatures (23 to 33°C); and direct contact of unprotected human skin with resulting filariform larvae. Infections become particularly intense in closed, densely populated communities, such as tea and coffee plantations. N. americanus is found in the tropical areas of South Asia, Africa, and America, as well as the southern United States, where it was introduced with the African slave trade. A. duodenale is seen in the Mediterranean basin, the Middle East, northern India, China, and Japan. It has been estimated that together these two worms extract over 7 million L of blood each day from 700 million individuals scattered around the globe, including 700,000 in the United States, leading to 50,000 to 60,000 deaths annually.

PATHOGENESIS AND IMMUNITY

Each adult A. duodenale extracts 0.2 mL of blood daily and N. americanus 0.03 mL of blood. Additional blood loss may be related to the tendency of the worms to migrate within the intestine, leaving bleeding points at old sites of attachment. Because the adults may survive 2 to 14 years, the accumulated blood loss may be enormous. The infection elicits both a humoral antibody response and immediate hypersensitivity reaction in the host, but evidence that these moderate the infection is lacking. The peripheral and gut eosinophilia characteristic of this disease may play a role in the destruction of worms and/or modulation of the immediate hypersensitivity reaction.

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