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The adult hookworm may remain alive in the intestine for as long as 6 years. The female Ancylostoma produces 25,000 to 35,000 eggs per day or up to 50-million in her lifetime; the female Necator is less productive, producing a mere 6,000 to 20,000 eggs per day. A certain amount of development occurs as each egg travels down the human alimentary canal. The eggs are identical for all species of hookworms and show a uniform oval contour, a thin transparent shell, an average size of 60 by 40-micra and possess 2, 4 or 8-embryonic cells when passed in stools (Fig. 12.5). If the feces are deposited in warm, moist, shaded soil with a temperature of 25-30ºC, the embryo becomes visible within the egg within 24-hours and escapes from it as a first-stage larva. Within 48-hours, it doubles in size, molts, and becomes a second-stage rhabditiform larva. Within a week after first hatching, it will again molt to become a third-stage or infective filariform larva while feeding upon the feces in moist earth or water (Fig. 12.6). It is active and can swim, wriggle or climb a moist surface. It can pass vertically through as much as 1-meter (3-feet) of light soil to reach the ground surface, where it may remain viable for up to 6-weeks in sandy or humus soil.

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Fig. 12.5 Two stages in the development of hookworm eggs. (A) Four cell stage. (Courtesy of Dr. Herman Zaiman, North Dakota.) (B) Embryonated egg showing a contracted larva. AFIP 56-3329.

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Fig. 12.6 Hookworm larvae. (A) Rhabditiform larva. X260. AFIP 56-3355. (B) Infective filariform larva (third stage) showing its protective envelope. X245. AFIP 56-3318.

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