Echinococcus multilocularis

The most common life cycle of E. multilocularis involves transmission between foxes (host to adult worm) and rodents as intermediate hosts (larval worm). Domestic dogs and cats can also become infected when eating infected rodents. Human infection occurs as a result of ingestion of tapeworm eggs by contamination of fox, dog, or cat faeces. The natural hosts are generally separated ecologically from humans. Infection of humans by E. multilocularis is less common than infections by E. granulosus. The primary localization of E. multilocularis larvae in humans, as well as in the natural intermediate hosts (rodents) is the liver. Local expansion of the lesion and metastases to the lungs and brain may follow. The typical lesion is a dispersed mass of fibrous tissue with a lot of scattered cavities ranging from a few millimetres to centimetres in size. In chronic cases, a central necrotic cavity can be formed, containing a viscous, yellowish to brown fluid, which may be superinfected. Metacestode proliferation is usually accompanied by a granulomatous host reaction and the induction of intense cellular inflammatory infiltration of the periparasitic hepatic area. The larval mass proliferates by exogenous budding of the germinative membrane, thus producing an alveolar like pattern of microvesicles. The invasion of surrounding tissues resembles cancer in behaviour and appearance. An entire hepatic lobe may be replaced by the larval lesion before the disease becomes clinically manifest. Scolices are rarely observed in infections of Echinococcus multilocularis in human (Gottstein and Hemphill 1997).

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