Most bloodthirsty parasite

The indistinguishable eggs of the hookworms Ancylostoma duodenale and Necator americanus are found in the faeces of 1.3 billion people worldwide. In cases of heavy infestation, the lining of the gut is so thickly covered with worms that they look like the pile of a carpet. The bleeding that results from their feeding adds up to a total of 10 million litres (2.2 UK gallon; 2.6 US million gal) of blood worldwide every day. Necator americanus, which ranges in size from 5–11mm (0.2–0.4 in), is responsible for about 90 percent of human hookworm infections that occur in tropical and subtropical regions of the world. Ancylostoma duodenale, 8–13 mm long, is found on all continents but is most prevalent in warm regions. A. duodenale possesses four hooklike teeth in its adult stage, and N. americanus has plates in its mouth rather than teeth. Both species of hookworm have similar life cycles. The adult worm attaches itself to the mucosal tissue lining the small intestine, where the female may produce several thousand eggs a day, which are passed in the feces. If the fecal matter reaches suitable soil, the eggs are hatched, and the infective, threadlike larvae may penetrate human skin, usually that of the foot, by way of the sweat glands and hair follicles. They then invade the lymph and blood vessels, reach the lungs, and pass up the respiratory tree to reach the mouth, where they are swallowed and sent to the small intestine; there they mature and start a new reproductive cycle. The intestinal parasites are reputedly long-lived, with a lifetime that may span some 10 years.