Hookworm larvae travel through the lungs before settling in the gut
A hookworm larva that bores into a bare foot takes a strange detour. It rides the bloodstream to the lungs, climbs the windpipe, gets coughed up and swallowed, and only then reaches the small intestine to mature. Five to nine weeks after entry, the adult worms are laying eggs.
Hookworms are blood-feeding parasitic roundworms of the intestine. They flourish where clean water, sanitation and hygiene are scarce, and in warm, rainy places where the soil stays damp, which makes rural coastal areas ideal. The link with poverty runs both ways: they are most common among the poor, and by harming children's health and schooling they help keep communities poor. They are the leading cause of anaemia and undernutrition in developing countries.
People are mainly infected by two species, Ancylostoma duodenale and Necator americanus. Ancylostoma is pale grey or pinkish, with a head bent slightly back to form the hook that names the group, and a mouth armed with two pairs of teeth; males are about 10 by 0.5 mm, females longer and stouter. Necator is smaller, males 5 to 9 mm and females around 10 mm, with a sharper hook and a pair of cutting plates instead of teeth. Many other hookworms target animals: cats, dogs and cattle each have their own, Ancylostoma ceylanicum spreads from pets to people in Asia, and at least 68 species are known from wild mammals.
Infection comes from larvae, not eggs. Eggs need warm, moist soil above 18 degrees Celsius to hatch, and larvae die in direct sun or if they dry out, though Necator tolerates more heat. The first two larval stages feed on faeces and soil microbes; after about a week they moult into a non-feeding infective stage that survives up to two weeks and crawls to higher ground to meet a host.
Necator can enter only through skin, while Ancylostoma can also be swallowed. Once inside, larvae reach the lungs through the circulation, break into the air sacs, move up the trachea and are swallowed, arriving in the gut after about a week. There they moult twice more into adults and mate.
Source: Hookworm
