First Occurrence of spp. (Nematoda: Dioctophymatidae) in a Subalpine Lake in Northwest Italy: New Data on Distribution and Host Range.

The genus includes nematodes that infect fish species and fish-eating birds inhabiting freshwater ecosystems. Nematodes belonging to the genus are potentially pathogenic for humans; infection occurs after the consumption of raw or undercooked fish. In the two-year period 2019-2020, a total of 292 fish belonging to eight species were examined for the occurrence of spp. from Lake San Michele, a small subalpine lake in northwest Italy. The prevalence of infestation was 18.3% in , 16.7% in , and 10% in . The other five fish species (, , , , and ) were all negative for parasite presence. There were no significant differences in prevalence between the three fish species (Fisher's exact test; = 0.744). The mean intensity of infestation ranged from 1 ( and ) to 1.15 (, and the mean abundance ranged from 0.1 () to 0.28 (). There were significant differences in the infestation site between the four muscle quadrants (anterior ventral, anterior dorsal, posterior ventral, and posterior dorsal) and the visceral cavity (Kruskal-Wallis test; = 0.0008). The study findings advance our knowledge about the distribution and host range of this parasite in Italy.