Fig. 12.3 Many adult A. duodenale attached to the duodenal mucosa. AFIP 75-14422. (Courtesy of Dr. Marcia Marchevsky, Rio de Janeiro).

Fig. 12.4 Adult hookworms clinging to small intestinal mucosa. (A) Photomicrograph showing longitudinal section of the head of a hookworm firmly attached to the jejunal mucosa. (B) Cross- section of A. duodenale in the small intestine showing its buccal capsule by which it attaches itself to the mucosa. AFIP 55-2261-3.


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Epidemiology and Pathology

For all practical purposes, hookworm infection in man results from the presence of adult A. duodenale and/or N. americanus within the small intestine, usually the jejunum and proximal ileum (Fig. 12.3). The worms firmly attach themselves to the intestinal mucosa where they suck blood, mucosal tissue and intestinal juices continuously to obtain necessary oxygen and glucose. The two principal species vary slightly in size and structure, with the adult female A. duodenale measuring 10 to 13 mm in length and 0.6 mm in diameter, whereas the male is 8 to 11 mm long and 0.45 mm wide. Both sexes attach themselves to the intestinal mucous membranes by their large buccal capsules, which contain both dorsal and ventral hooked teeth in Ancylostoma and a pair of cutting plates in Necator (Fig. 12.4). Necator americanus is a shorter and more slender worm, with the female measuring 9 to 11 mm in length by 0.35 mm in width and the male being 5 to 9 mm long by 0.3 mm wide. Adult hookworms are creamy white in color when alive but gray when dead. When engorged with blood, they are reddish-brown.

There are other ancylostomes (A. ceylanicum, A. braziliense, A. caninum, and A. malayanum), which are normally parasitic in animals, but occasionally invade man. They may cause a localized skin eruption but usually do not undergo full development in their human hosts. There has been a 1988 report of Löffler syndrome associated with ancylostomiasis brasiliensis and a 1994 report of A. caninum (Ann Int Med 120:434, 1994) causing an eosinophilic enteritis resulting in pain, diarrhea, rectal bleeding, weight loss, and abdominal distention.


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