N. americanus larvae must penetrate the skin directly, while A. duodenale infections can be percutaneous, oral, transmammary, and probably placental.


Eggs are passed in the stool (1) , and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days. The released rhabditiform larvae grow in the feces and/or the soil (2) , and after 5 to 10 days (and two molts) they become become filariform (third-stage) larvae that are infective (3). These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the human host, the larvae penetrate the skin and are carried through the veins to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed (4). The larvae reach the small intestine, where they reside and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host (5). Most adult worms are eliminated in 1 to 2 years, but longevity records can reach several years.
Some A. duodenale larvae, following penetration of the host skin, can become dormant (in the intestine or muscle). In addition, infection by A. duodenale may probably also occur by the oral and transmammary route. N. americanus, however, requires a transpulmonary migration phase.


There is no known reservoir, although laboratory tests have shown that certain animals (rabbits, lambs, calves, and pigs) can act as paratenic hosts when fed infective larvae of A. duodenale, and are then infective when fed to puppies (Markell 285).

Animal hookworms (A. braziliense, Uncinaria stenocephala) may penetrate human skin causing cutaneous larva migrans but then cease to develop. Alternatively, the animal hookworm A. ceylanicum may parasitize humans.

none, larvae infect host directly