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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.


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.


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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