Echinococcosis is a parasitic disease that occurs in two main forms in humans: cystic echinococcosis (also known as hydatidosis) and alveolar echinococcosis, caused by the tapeworms Echinococcus granulosus and Echinococcus multilocularis, respectively.
Dogs, foxes and other carnivores harbour the adult worms in their intestine and evacuate the parasite eggs in their faeces. If the eggs are ingested by humans, they develop into larvae in several organs, mainly the liver and lungs.
Both cystic and alveolar echinococcosis are characterized by asymptomatic incubation periods that can last many years until the parasite larvae evolve and trigger clinical signs.
Both diseases can cause serious morbidity and death.
A number of herbivorous and omnivorous animals act as intermediate hosts of Echinococcus by ingesting parasite eggs in contaminated soil and developing parasitic larval stages in their viscera. Carnivores are definitive hosts of the parasite; they are infected through the consumption of viscera of intermediate hosts that harbour the parasite and also through scavenging infected carcases. Humans are accidental intermediate hosts and are unable to transmit the disease.
Transmission of cystic echinococcosis is principally maintained in a dog–sheep–dog cycle, although several other domestic animals may be involved including goats, swine, horses, cattle, camels and yaks. Transmission of alveolar echinococcosis usually occurs in a wildlife cycle among foxes, other carnivores and small mammals (mostly rodents). Domesticated dogs and cats can also be infected.
For both diseases, humans become infected through the ingestion of soil, water or food (e.g. green vegetables, berries) contaminated with the parasites’ eggs shed in the faeces of the carnivores, and also by hand-to-mouth transfer of eggs after contact with the contaminated fur of a carnivore, most commonly a dog.
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