Genetic diversity, haplotype structure, and population dynamics of Echinococcus granulosus isolates from human cystic...

Cystic echinococcosis (CE) is a globally important zoonotic disease caused by the larval (metacestode) stage of Echinococcus granulosus (sensu lato), a parasite complex characterized by marked genetic heterogeneity across geographical regions. The Tibet Autonomous Region (TAR) of China is one of the most hyperendemic areas for human echinococcosis, yet information on the genetic diversity and population structure of human-derived E. granulosus isolates remains limited. This study aimed to characterize the genetic diversity, haplotype distribution, and population dynamics of E. granulosus isolates from human CE cases in TAR, thereby improving understanding of parasite transmission in this unique epidemiological setting.

Between 2018 and 2019, hydatid cyst samples were collected from 54 patients with confirmed CE in echinococcosis-designated hospitals across five prefectures (Shigatse, Nagqu, Shannan, Nyingchi, and Qamdo) of TAR. Species identification and genotyping were performed using mitochondrial cytochrome c oxidase subunit 2 (COX2) and nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 1 (NADH1) genes. Phylogenetic relationships were inferred using the neighbor-joining method, haplotype networks were constructed using PopART, and population genetic indices and neutrality tests were applied to assess genetic diversity and demographic history.

All 54 isolates were successfully amplified and sequenced for COX2, while 50 isolates were analyzed for NADH1. Phylogenetic analysis identified three circulating E. granulosus (s.l.) genotypes: G1 (sheep strain), which predominated, along with G3 (buffalo strain) and G6 (camel strain). Notably, this study reports, for the first time, the presence of the G3 genotype in human isolates from multiple prefectures in Tibet. Haplotype analysis revealed high haplotype diversity (Hd = 0.771 ± 0.00323) and low nucleotide diversity (π = 0.00736 ± 0.00411), forming a star-like haplotype network (n = 20) centered on a dominant haplotype (H2) based on COX2 sequences. Significantly negative Tajima's D and Fu's Fs values indicate recent population expansion.

This study provides the first comprehensive insight into the genetic structure and population dynamics of human-derived E. granulosus isolates in TAR. The observed high genetic diversity, presence of multiple zoonotic genotypes, and evidence of population expansion suggest active and widespread transmission on the Tibet Plateau, underscoring the need for integrated, region-specific control strategies within a One Health framework.