Low genetic variation in Echinococcus multilocularis from the Western Sichuan Plateau of China revealed by microsatellite and mitochondrial DNA markers

The prevalence of E. multilocularis is a major public health problem in China. To better understand the molecular epidemiology and evolutionary patterns of E. multilocularis, an adequate dataset regarding the genetic variance of this parasite is necessary. However, for now, available genetic data of E. multilocularis is still insufficient. In the study, the EmsB microsatellite and the partial mitochondrial cox1 gene were combined to investigate the genetic diversity of 64 E. multilocularis samples from human, dogs and voles. These samples were collected in the Western Sichuan Plateau, where the highest village-based human prevalence of alveolar echinococcosis was recorded worldwide. The aim of the study is to gather more informative genetic data of E. multilocularis in the areas, especially those obtained using the EmsB marker. The microsatellite analysis revealed 7 different EmsB profiles, 1 of which was found in 90.63% of the total samples collected from all 3 hosts. This major profile was identical to the one detected in the same area 16 years ago. The rest of the 6 profiles, each represented by only 1 isolate, did not correspond to any of the profiles previously reported. All the profiles detected in the study belonged to the Asian cluster. Meanwhile, according to sequence analysis of the 758 bp cox1 region, 4 haplotypes all assigned to the Asian clade were detected among the isolates. A star-like haplotype network was exhibited with a centrally positioned haplotype found in 93.75% of the samples. The overall haplotype and nucleotide diversities were both low. These findings provided evidence for a founder event or bottleneck and subsequent population expansion in E. multilocularis. The EmsB profiles were not fully consistent with the cox1 haplotypes. The same correspondence relationship was mainly observed in samples with the major profile P5 and the main haplotype EmHa1. A total of 54 isolates assigned to profile P5 were classified to the EmHa1 haplotype. In conclusion, both the microsatellite and mtDNA markers showed low variability within the Tibetan population of E. multilocularis. An EmsB profile and a cox1 haplotype were found to be predominant in the study area, which appears to remain steady for over a decade. The results reinforce the higher potential of the microsatellite DNA marker with high discriminative power to identify the very low genetic polymorphism of E. multilocularis than that of the partial cox1 sequencing. The data obtained in the study would be helpful to enlarge the data pool to further probe the possible origins and dispersal of E. multilocularis in China.