Hookworm Infection – Etiology And Epidemiology
Etiology - These diseases are produced by certain species of hookworms which parasitizes man: Necator americanus, the so-called American hookworm: Ancylostoma duodenale, the so-called Old World hookworm; and the Ancylostoma braziliense.The first two are exclusively parasites of man; A.braziliense is normally a parasite of dogs and cats.These worms are 7.5 to 13 mm.long and 0.3 to 0.4 mm.in greatest breadth.
The mouth of Necator is provided with a pair of upper and a pair of lower cutting plates; that of Ancylostoma, with tow or three pairs of upper teeth.The females have a bluntly pointed caudal extremity and a vulvar opening midventral in position near the equatorial plane.The caudal extremity of the male is drawn out into an umbrella-like expansion, the copulatory bursa.These worms are attached by their mouth capsule to the mucosa of the small bowel, typically at the level of the duodenum, jejunum, and adjacent portion of the ileum.
After insemination each female hookworm lays several thousand eggs a day.These eggs are broadly ovoidal, thin-shelled and hyaline and measure 60 to 76 by 36 to 40 microns.They are usually in an early stage of development when evacuated, but in constipated stools may be more advanced in their development.
Epidemiology – Necator americanus is the tropical hookworm of the Eastern Hemisphere; it is the only widely distributed hookworm in the Americas, including the southern United States.Ancylostoma duodenale is the hookworm of the Mediterranean basin and similar latitudes in Asia and is the more common species on the Pacific coast of South Africa.Ancylostoma braziliense has a spotted distribution in warm climates.Intestinal infection with this species appears to be limited almost exclusively to canine and feline hosts.
When eggs of Necator and A.duodenale are evacuated from the human bowel and deposited on a moist, sandy humus soil in a shaded site in warm climates, they embryonate rapidly and hatch in twenty-four to forty-eight hours.The escaping larvae feed ravenously on bacteria and organic debris, grow, moult, feed again and, between the fifth and tents days, transform into infective-stage larvae.
Human exposure occurs when these third-stage larvae come in contact with the skin, as when persons walk barefooted on or handle infected soil.Infants and small children are seldom exposed to infection except in hyperendemic areas.Older children and young adults, especially males, are most frequently parasitized and in highly endemic areas are subject to repeated infection.Thus man initiates the extrinsic phase of the life cycle by discharging hookworm eggs on the soil and, in turn, picks up the infection by direct contact with the soil.
The human, canine and feline strains of A.braziliense are physiologically distinct.Man acquires intestinal infection from the human strain, and cutaneous larva migrans (creeping eruption) from canine or feline strains (Ernest Carroll Faust).Do you find this article helpful? Thank you in advance.