Genome-wide population genomic analyses reveal extensive admixture and limited geographic structure in Australian Fasciola hepatica.

Fasciola hepatica is a globally important trematode parasite of livestock and humans, but its population structure in Australia remains unknown. In this study, double-digest restriction site-associated DNA sequencing (ddRADseq) was used to investigate population genomic structure and genetic diversity in 217 adult F. hepatica collected from cattle and sheep across New South Wales (NSW), Victoria (VIC) and Tasmania (TAS). After quality filtering and linkage disequilibrium pruning, 9,205 single nucleotide polymorphisms (SNPs) were retained for analyses. Principal component analysis (PCA), fastSTRUCTURE and identity-by-state (IBS) analyses consistently revealed weak geographic structuring and extensive admixture among populations from southeast Australia. Although differentiated clusters were detected in Sunny Corner (NSW), with three Echuca (VIC) individuals also showing separation from the main cluster and a subset of Powranna (TAS) and Numbugga (NSW) individuals showing partial differentiation, most individuals exhibited substantial genetic overlap across populations. This genome-wide analysis provides an important genomic framework for future surveillance and improved understanding of the population biology and epidemiology of fascioliasis in Australia.