Thelazia rhodesi and Thelazia skrjabini in wild European bison (Bison bonasus) and farmed American bison (Bison bison) from Romania, 2021-23.

Between November 2021 and January 2023, the eyes of either slaughtered or deceased male American bison (Bison bison) and European bison (Bison bonasus) from Romania were investigated for the presence of Thelazia spp. nematodes (eye worms). These included seven farmed American bison from two locations and two wild European bison from reintroduction sites. Thelazia rhodesi and Thelazia skrjabini were present in three American bison and both European bison. A total of 38 nematodes were recovered, with T. rhodesi being the predominant species. Molecular analysis confirmed these findings and identified unique sequences for both species. The nematodes in American bison were distributed across the Pannonian and Continental biogeoregions, and those in European bison originated from the Alpine region. Thelazia spp. have not previously been reported in American bison, nor in European bison from Romania. The findings underscore the need for continuous monitoring and management of Thelazia infections to support conservation and reintroduction efforts. Future research should focus on the ecological factors influencing these infections and develop strategies to mitigate their impact on wildlife health.