The genetic variation of mitochondrial sequences and pathological differences of Echinococcus multilocularis strains from different continents.

Alveolar echinococcosis is a lethal zoonotic disease caused by the fox tapeworm Echinococcus multilocularis. The parasite is widely distributed in the Northern Hemisphere and exhibits low genetic diversity among populations. To compare the differences among four E. multilocularis strains from different geographical locations, namely, Alaska (EM-AK), Japan (EM-JP), Xinjiang (EM-XJ), and Ningxia (EM-NX), their complete mitochondrial (mt) sequences were compared, and their induced pathological lesions were analyzed in mouse models. The complete mt sequence of EM-AK resulted in 0.84%-0.86% variation as compared with the other strains, which had a lower variation. Phylogenetic analysis and parsimony network indicated that EM-AK resulted in 30,000 years of evolutionary distance from the other three strains. EM-AK induced more pathological damage than the other three strains, which was likely to induce more host cell infiltration and acute granuloma in the liver. More importantly, EM-AK produced more protoscoleces than the other three strains, which may impact the transmission dynamics of the parasite. Given the geographical location of four strains, which is far from each other, and also the pathological differences, the strains of E. multilocularis are likely models for addressing the relationship and interfacial immune response between the host and the helminth.IMPORTANCEEchinococcus multilocularis is the causative agent of alveolar echinococcosis, which is considered the most serious parasitic disease in the Northern Hemisphere. There are many genotypes, but the pathogenic and mitochondria sequence and differences are still unclear. Therefore, this study showed both pathological and genetic differences between the four strains of E. multilocularis. EM-AK induced more severe immune responses and especially induced more host cell infiltration, which resulted in more severe granuloma in the liver. EM-JP has metacestode lesions morphologically closer to those of E. granulosus with clear cyst fluid. However, this strain produced much fewer protoscoleces (PSCs). Genetically, EM-AK is more distant from other strains.