Echinococcosis is a debilitating tapeworm infection of humans and animals (particularly sheep and dogs), caused by the parasitic larvae of the tapeworm Echinococcis spp. Humans become infected by swallowing the eggs of helminths, mostly after touching dogs. Larvae emerge from the eggs in the intestine, penetrate into the blood vessels, and are carried to various organs (mainly liver and lungs), where they change into hybrid cysts.
Echinococcosis was described during the time of Hippocrates (460-379 BC), and during the Middle Ages it was regarded as being a condition of degenerated glands, collections of pus, or distended lymph spaces. It was not until the middle of the 19th century that its actual nature as a tapeworm disease became known.