Alveolar echinococcosis is caused by infection with Echinococcus multilocularis. The definitive hosts are foxes, coyotes, and dogs. Small rodents act as intermediate hosts. After a long asymptomatic incubation period lasting 5-15 years, the infection produces a primary tumor-like lesion usually in the liver. The patient often presents with weight loss, abdominal pain, malaise and signs of hepatic failure. The larvae may spread locally to spleen and adjacent organs or to distant sites such as lung and brain. In the absence of treatment, alveolar echinococcosis is progressive and fatal. Radical surgery followed by anti-infective prophylaxis offers the best chance for cure. Image copyright: pathorama.ch.