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

Abstract

The genus <i>Eustrongylides</i> includes nematodes that infect fish species and fish-eating birds inhabiting freshwater ecosystems. Nematodes belonging to the genus <i>Eustrongylides</i> 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 <i>Eustrongylides</i> spp. from Lake San Michele, a small subalpine lake in northwest Italy. The prevalence of infestation was 18.3% in <i>Lepomis gibbosus</i>, 16.7% in <i>Micropterus salmoides</i>, and 10% in <i>Perca fluviatilis</i>. The other five fish species (<i>Ameiurus melas</i>, <i>Ictalurus punctatus</i>, <i>Squalius cephalus</i>, <i>Carassius carassius</i>, and <i>Scardinius erythrophthalmus</i>) were all negative for parasite presence. There were no significant differences in prevalence between the three fish species (Fisher's exact test; <i>p</i> = 0.744). The mean intensity of infestation ranged from 1 (<i>M. salmoides</i> and <i>P. fluviatilis</i>) to 1.15 (<i>L. gibbosus)</i>, and the mean abundance ranged from 0.1 (<i>P. fluviatilis</i>) to 0.28 (<i>L. gibbosus</i>). 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; <i>p</i> = 0.0008). The study findings advance our knowledge about the distribution and host range of this parasite in Italy.