This disease is characterized in humans by the appearance of cysts that are really the larval stage of the Echinococcus tapeworm, found in the adult stage in dogs and other carnivores.
It is present all over Spain, mainly in La Rioja, Navarre, Madrid, Castile and León and Castile-La Mancha.
The definitive hosts of the worm are domestic dogs and some wild canids, and the intermediate hosts are herbivores and omnivores (especially sheep, goats and cows).
Adult tapeworms live attached to the small intestine of dogs or other definitive hosts, measure between three and six millimetres in length and have three or four proglottids (segments) of which the last one is gravid and contains between 200 and 800 eggs. It is calculated that they come loose every 15 days and are passed through the faeces. Once in the environment, the proglottid disintegrates and frees its load of hundreds of microscopic eggs that cause the cycle to begin again when they are ingested by the intermediate host.
When the intermediate host ingests the eggs of the Echinococcus granulosus tapeworm the larval stage or hydatid cyst develops. These cysts are usually located in the liver or lungs and, less frequently, in the kidneys, heart, central nervous system or bones.
Humans are accidental intermediate hosts who may acquire the disease through direct contact with infected dogs or indirectly by drinking water, eating vegetables or by contact with objects contaminated by the faeces of domestic dogs or wild canids infected by the parasites.
The symptoms depend on the location and size of the cysts, which develop very slowly and may grow to a diameter of 10 cm.
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