An intestinal roundworm infestation that may cause diarrhoea and abdominal pain
The roundworm Ascaris lumbricoides is responsible for ascariasis, one of the most common parasitic infestations of humans. About 1 in 4 people in the world has ascariasis at some time in his or her life. The disease is most common in tropical and subtropical areas, and children are affected more often than adults. Ascariasis is rare in developed countries such as the UK.
People usually become infested with roundworms by eating food or drinking water contaminated with the worm eggs. Poor sanitation, the use of human excrement as fertilizer and inadequate personal hygiene all contribute to the spread of ascariasis among humans. Once swallowed, the worm eggs hatch into larvae in the intestine. The larvae then travel in the blood to the lungs and later return to the intestine, where they develop into adults, breed, and lay eggs.
In most cases, ascariasis does not cause symptoms. However, in large numbers, the roundworms may cause:
Ascariasis is usually diagnosed by identification of the worm eggs in a sample of faeces or of the worm itself, which is pale pink and has a long cylindrical body approximately 20–30 cm (8–12 in) in length. Treatment is with anthelmintic drugs to kill the worms. However, the infestation will recur if roundworm eggs are swallowed again after treatment.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.