Conserved Hepatospora eriocheir Sequences in Chinese Mitten Crabs from Poland, Germany and Belgium: A Comparative Molecular Study

Hepatospora eriocheir is an obligate intracellular microsporidian associated with the Chinese mitten crab, Eriocheir sinensis, an important aquaculture species in Asia and an invasive species in Europe. We investigated parasite sequence variation in crabs from three European regions: the Vistula Lagoon in the Baltic Sea (Poland) and the Elbe and Scheldt catchments draining into the North Sea (Germany and Belgium). Among 57 crabs examined, 26 infections were confirmed by small subunit ribosomal RNA (SSU rRNA) sequencing, including 17 newly identified infections among 42 specimens collected in 2022. The parasite groups comprised 13 Polish, eight German and five Belgian infections. Their SSU rRNA sequences were identical across a 794-position shared core, and all 26 newly generated arginyl-tRNA synthetase (ArgRS) sequences were identical across 624 nucleotides and matched the British reference KU695717. Both parasite gene fragments were identical across four host mitochondrial cytochrome c oxidase subunit I (COI) haplotypes; the Eriocheir japonica-associated haplotype was detected only in Belgian crabs in this sample. The study provides the first specimen-linked, sequence-confirmed molecular characterisation of infections in the sampled German and Belgian crab populations, together with new Polish infections from 2022 and a comparative two-locus reference dataset. The repeated Baltic detection, combined with shared Polish–German host COI haplotypes and existing evidence of North Sea–Baltic connectivity, is consistent with the arrival of infected migrating crabs, although the parasite’s precise source remains unresolved.