Internal parasites of the Eurasian beaver (Castor fiber) in Lesser Poland region (Poland) - occurrence and diversity

Between 2017 and 2019, necropsies were performed on 26 Eurasian beavers ( Castor fiber ) from the Lesser Poland Voivodeship (Małopolska Region), Poland, to investigate the composition of their helminth fauna. Two host-specific helminth species were identified - Stichorchis subtriquetrus and Travassosius rufus . Trematode S. subtriquetrus was more prevalent, infecting 88.5% of beavers (95% CI: 69.8-97.6%) with a mean intensity of 132.7 ± 114.7 parasites per host (range: 2-454), whereas nematode T. rufus occurred in 69.2% of hosts (95% CI: 48.2-85.7%), with a mean intensity of 306.7 ± 493.3 (range: 7-2057). The abundance of neither S. subtriquetrus nor T. rufus was significantly associated with host sex, body mass, age or landscape type, season, and site (p > 0.05). Likewise, no significant correlation was found between the abundances of the two helminth species (p > 0.05). In contrast, the numbers of male and female T. rufus recovered from individual hosts were strongly positively correlated (r = 0.98, p < 0.001), with females consistently predominating. These findings are consistent with previous studies reporting the dominance of these species in beavers.