Guinea worms are endemic to Africa, India and the Middle East. They are large and conspicuous worms (female worms can reach up to 80 cm in length) and have been a cause of human suffering since antiquity.
People become infected when they drink unfiltered water containing tiny crustaceans (copepods) infected with the larval stage of the worm. The larvae penetrate through the infected person’s small intestine, then migrate through the abdominal muscles to reach the connective tissue above the muscle layer. The worms moult and develop to maturity and females become fertilised after mating with male worms.
Mature female worms then migrate through the connective tissue to just beneath the skin, often in the legs of their host. An allergic reaction, in response to release of the juvenile worms, causes an ulcerative blister to form at the site. This painful blister is relieved somewhat by immersion in water but contact with water also stimulates the female worm to release more juveniles. The site of the blister is prone to secondary bacterial infection so that abscesses may form.
Sometimes adult worms fail to reach the skin. If they are caught in the deeper tissues around the joints it may lead to chronic arthritis. If caught in the nerves of the spine they can cause paralysis of the legs (paraplegia).
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