© Solange BRESSON

Alveolar echinococcosis in Switzerland

Alveolar echinococcosis (AE), a hepatic disorder caused by the continuous proliferation of the Echinococcus multilocularis metacestode (larvae), is one of the most potentially dangerous parasitic zoonosis in Europe. Its proliferative progression is very comparable to a slow growing liver cancer and, if left untreated, the 10-year mortality rate can reach up to 90%. Although still a rare disease, cases are increasing in the endemic area of Central Europe. Moreover, the geographical distribution of the parasite and the occurrence of human AE cases is expanding to countries previously considered AE free. After a short review of the current epidemiological situation of AE worldwide and its current presentation and management modalities in Western countries, we will focus on the situation in Switzerland.

The main definitive hosts are foxes, less commonly dogs and other canids, harboring small (few millimeters in length) adult stage tapeworms in their small intestine. Parasite eggs are disseminated into the environment via feces. Natural intermediate hosts harboring larval stages in their liver are small rodents. Infection of these hosts occurs upon ingestion of infectious Echinococcus multilocularis eggs, which hatch in the intestine to release oncospheres that pass through the portal and lymphatic vessels to reach the liver, where they usually settle and develop as metacestodes (larvae). Humans are accidental “intermediate” hosts and a dead end for the parasitic life cycle. Infection of humans seems to occur mainly by ingestion of contaminated raw vegetables, wild berries, wild plants or by direct contact with an infected definitive host (Fig.1). Echinococcus multilocularis eggs can remain infective for months and up to a year, depending on environmental conditions. The eggs are sensitive to dehydration and heat but can survive freezing at –20°C.1 Anatomically, the parasitic lesion in the liver is an infiltrative mass consisting of multiple alveoli (Fig. 2). Microscopically, Echinococcus multilocularis produces alveolar microcysts that grow by exogenous proliferation. Distant metastases via hematogenous spread of viable metacestode fragments are possible, affecting mainly the lungs, more rarely the brain or other organs. In humans, the slow development of the metacestode is accompanied by an intense granulomatous reaction, which, with time, can develop into extensive fibrosis leading to obstructive complications. Metacestodes may also become inactive in some cases.

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