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Echinococcus multilocularis

Common name. The hydatid worm

Disease. Hydatid disease, Hydatidosis, Alveolar (multilocular) hydatid disease

Geographic distribution. Primarily in Europe, Asia, New Zealand, and South/North America.

Infection rate. Human infection with alveolar hydatid cyst is rare.

Life cycle. Foxes, dogs, and cats are the definitive hosts. The hydatid cysts develop in several species of small rodents. The life cycle is similar to that of E. granulosus.

Morphology. The adult worms are similar to E. granulosus with smaller body lengths of 1.2 ㎜ ~ 3.7 ㎜. Cyst has a thin outer wall that grows and infiltrates into the surrounding host tissues. Fluid-filled pockets containing protoscolices may be produced. The cysts break off and metastasize to other parts of the body, forming alveolar or multilocular hydatid cysts in humans.

Pathology and clinical sysptoms. The cyst grows very slowly and metastases occur by direct extension or via the blood or lymphatic system. The liver is most frequently involved organ in humans. Hepatomegaly, reduced liver function, obstrucion of bile duct and portal vein, and ascites can be seen.

Diagnosis. Diagnosis of alveolar hydatidosis is difficult due to the lacking of protoscolices in the cysts. Radiological studies or ELISA can be helpful.

Prevention. Deworming of dogs are preventive ways in the endemic regions.

Duk-Young Min

Multilocular hydatid cyst of Echinococcus multilocularis (H&E, 400x).

DY Min/MH Ahn/JS Ryu