One quarter of the entire population of the world is affected by hookworm (Ancylostomiasis), which is an infestation of the gut by the nematode worm Ancylostoma duodenale.
The eggs of the adult hookworm, which is 1 cm long, pass out in the faeces, and if the faeces fall onto moist ground, the larvae will hatch from the eggs. The larvae remain active in moist soil for up to a week, and during that time, a larva may penetrate the skin of the foot of any person who treads on it. The larva then migrates through the bloodstream to the lung, where it breaks into the air-carrying passageways of the lung. From there it is carried with sputum up into the throat, where it is swallowed, enters the gut, develops into an adult worm and starts the process all over again. It may be caught in all the tropical countries of the world.
Patients develop an itch at the site of skin penetration, a cough, wheeze and fever while the larvae are in the lung, and mild abdominal discomfort and diarrhoea when there are a large number of worms in the gut, but only in patients who are otherwise ill or malnourished does a hookworm infestation cause significant problems
Examination of a sample of faeces under a microscope reveals the worm or its eggs, and drugs are available to successfully destroy the worms.