First Report of Haplosporidium edule Infection in the Olive-Green Cockle (Cerastoderma glaucum) from the Northern Adriatic Sea: Expanding Host Range and Geographic Distribution

Haplosporidium edule is a haplosporidian parasite originally described in the common edi-ble cockle (Cerastoderma edule) along the European Atlantic coast. In this study, we report the first detection of H. edule in the olive-green cockle (Cerastoderma glaucum) from the northern Adriatic Sea, representing both a novel host record and a new geographic occur-rence. During a cross-sectional study conducted in May 2019, 90 C. glaucum specimens were collected from three lagoon sites in northeastern Italy. Histological examination of soft tissues revealed haplosporidian developmental stages, including plasmodia, sporo-blasts and mature spores, within connective tissues of the mantle, digestive gland, gills and between gonadal tubules in eight individuals from the Goro Lagoon. Molecular char-acterization based on a fragment of the small subunit ribosomal DNA showed high simi-larity with the previously published H. edule sequence. Host identification was confirmed through cytochrome c oxidase subunit I barcoding together with morphological and histo-logical analyses. These findings indicate that H. edule has a broader host range than pre-viously recognized. Although prevalence was relatively low, the detection of this parasite in a new host species and geographic area highlights the importance of continued surveil-lance, particularly in the context of climate change, shellfish translocations and the expan-sion of aquaculture activities.