Échinococcose alvéolaire

Abstract

Alveolar echinococcosis is caused by the larva of the cestode Echinococcocus (E.) multilocularis. Carnivores, typically foxes, but also domestic dogs and cats are definitive hosts, harbouring the small adult tapeworms in their intestine. Many species of rodents act as intermediate hosts, allowing the liver development of the metacestode (larval stage) of E. multilocularis. Human is an aberrant host for the metacestode. Contamination occurs either by eating vegetables or wild berries tainted by the infected feces of the carnivores, or by touching these animals. This disease is observed only in the temperate northern hemisphere. The main endemic area are Alaska, Japan, China, Russia , Central Asia, Western Turkey and Central Europe. New factors seem to currently modify the epidemiology of alveolar echinococcosis and to cause an extension of the disease in new areas. Increasing fox populations, invasion of cities by foxes, probably contribute to these changes. The role of cellular immunity in the immune response against E. multilocularis larvae has been clearly established. A spontaneous secretion of IL-10 by the peripheral blood mononuclear cells and within the periparasitic granuloma is the immunological hallmark of patients with progressive forms of the disease. Genetic correlates of resistance or susceptibility to human alveolar echinococcosis have been indicated by analysis of human leucocyte antigen markers in a large group of European alveolar echinococcosis patients. Human alveolar echinococcosis is a potentially fatal, chronically progressive hepatic disease, that is characterized by a long asymptomatic period in which development of an invasive-tumour-like multi-vesiculated lesion occur. Vascular and biliary structures as well as adjacent organs may be involved in the parasitic process. There is, in addition, a risk of hematogenous spreading resulting in distant metastases. Unusually for a parasitic helminth infection, it is a life-threatening disease. Efficient drugs able to destroy the larva are currently lacking. A partial surgical resection is the only curative treatment in case of a rather limited disease, a situation which becomes more frequent due to the large use of abdominal ultrasonography. In case of large unresectable lesions, long-term administration of the parasitostatic benzimidazole derivates, albendazole or mebendazole and use of interventional radiology procedures are now able to stabilize the patients. Liver transplantation had been undertaken in some patients with very severe alveolar echinococcosis, mainly due to biliary complications. This ultimate therapeutic option must be preceded by a meticulous evaluation to identify extra-hepatic extension and need to be associated with long term benzimidazole therapy. Finally, the better comprehension of the immunopathogenesis of this disease allows to consider therapeutic immunomodulation for alveolar echinococcosis in the future.