A rare infestation of tapeworm cysts that may affect the liver, lungs, or bones
- Infestation usually occurs in children but normally becomes apparent in adults
- Owning pet dogs may be a risk factor
- Gender and genetics are not significant factors
Infestation with cysts that contain the larvae (immature stages) of the tapeworm Echinococcus granulosus is called hydatid disease. The cyst stage of the worm normally affects livestock such as sheep. If a dog eats raw offal containing a cyst, the larvae mature into egg-laying adults in the dog’s intestines. Worm eggs pass out in the dog’s faeces and can be transmitted to humans who eat food that is contaminated with eggs. The eggs hatch into larvae when they reach the human intestine. The larvae then move to the liver, lungs, or bones, where they develop into slow-growing cysts up to 20 cm (8 in) in diameter.
Hydatid disease occurs most commonly in sheep-farming regions where sheepdogs are used, such as Australia, New Zealand, and, to a lesser extent, the UK. The infestation also occurs in Middle Eastern countries.
What are the symptoms?
Infestation mainly occurs in childhood, but symptoms may not develop until adulthood because the hydatid cysts are so slow-growing. In many cases, there are no symptoms. However, a hydatid cyst in the liver may cause:
Yellowing of the skin and whites of the eyes (see Jaundice).
A cyst in the lungs may lead to chest pain and coughing, and a cyst in bone may cause pain and fractures in the long bones of the limbs.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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