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Echinococcus multilocularis is a tapeworm with zoonotic potential that is common in the northern hemisphere. Its natural definitive hosts are foxes and other canids and its intermediate hosts are rodents. Other mammalian species, including man, can become infected and develop infiltrative, tumour-like lesions that particularly affect the liver. The present study characterizes the relatively rare lesions of alveolar echinococcosis in 10 dogs. Metacestodes in these dogs frequently contained no protoscolices and were thus sterile. Metacestodes were surrounded by fibrous tissue intermixed with inflammatory cells comprising variable numbers of macrophages, T and B lymphocytes, and plasma cells, as well as neutrophils and/or eosinophils. These lesions resemble those observed in man and are in contrast to those observed in the natural intermediate hosts, which have less fibrosis and more protoscolices.