Folia Parasitologica 72:003 (2025) | DOI: 10.14411/fp.2025.003

Potentially zoonotic parasite arrives to continental France: Clinostomum complanatum (Trematoda: Digenea) infection in perch (Perca fluviatilis) from the Doubs River (Jura)

Eloïse C. Rochat ORCID...^{1, 2}, Pierre Marle ORCID...³, Françoise Pozet ORCID...⁴, Isabel Blasco-Costa ORCID...^{1, 2*}

¹ Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway;

² Natural History Museum of Geneva, Switzerland;

³ Laboratory of Aquatic Ecology and Biology, Institute for Environmental Sciences, Department F.-A. Forel for Environmental and Aquatic Sciences, Earth and Environment Sciences, University of Geneva, Switzerland;

⁴ Departmental Analysis Laboratory of Jura, Poligny Cedex 2, France

^* Address for correspondence: I. Blasco-Costa, Natural History Museum of Geneva, Route de Malagnou 1, 1208 Geneva, Switzerland. Phone: +41 22 418 6387; Email: isabel.blasco-costa@geneve.ch; ORCID-iD: 0000-0002-5001-5986

Clinostomum complanatum (Rudolphi, 1814) is known as a food-borne zoonotic parasite using freshwater fish as intermediate host, although in its native distribution area in Europe, the Danube and Po basins and the northeast of Italy, no cases have been reported. This study reports a new geographic location outside the native distribution range of this parasite. We detected high infection levels of C. complanatum in wild perch (Perca fluviatilis Linnaeus) from the Doubs River in continental France. Clinostomum complanatum reached a prevalence of 97% and mean intensity of 5.8 cysts per fish in 33 fish examined, with most fish already infected by the age of two years. No correlations were observed between fish traits (standard length, weight, age and sex) and the number of parasites. The distribution of C. complanatum cysts in the fish body was not random. The tissue surrounding the opercula and branchial cavity, and muscles along the lateral line and near the pectoral, dorsal and caudal fins were the preferred sites of infection. Morphological identification was confirmed with molecular data. The French specimens shared identical mt cox1 haplotypes with specimens from Italy. The distribution of this exotic parasite in freshwaters in continental France deserves further research. Under the current French law, the parasite occurrence represents an economic loss for the local freshwater aquaculture industry, and a possible zoonotic risk for consumers if undetected, especially when raw or marinated fish is consumed. We provided a list of all reported hosts for C. complanatum from the western Palaearctic, discussed the knowledge gap regarding the zoonotic risk of C. complanatum in Europe, and highlighted the lack of policy that may increase the hazards posed by food-borne emerging parasites and their broader ecological impacts as alien species in freshwaters in Europe.

Keywords: Platyhelminthes, alien species, Halzoun syndrome, food-borne disease, freshwater ecosystems, cytochrome c oxidase subunit I mitochondrial gene, 28S rRNA gene

Received: July 23, 2024; Revised: September 28, 2024; Accepted: October 2, 2024; Published online: January 17, 2025  Show citation