Trypanosomatids in European bison (Bison bonasus): insights from biting midges and tissue screening

While leishmaniases have long been established in southern Europe, increasing cases have also been reported in Central Europe. A recent serological study in Poland suggested the presence of Leishmania spp. in European bison ( Bison bonasus ). To verify this, we screened both Culicoides biting midges and European bison tissues for Leishmania DNA. Biting midges were collected in the Białowieska Forest, where we identified ten species, with Culicoides obsoletus and C. pictipennis being the most abundant. However, none of the 129 biting midges or 63 European bison tissue samples tested positive for Leishmania DNA. In contrast, Culicoides midges were found to carry Trypanosoma theileri and the monoxenous trypanosomatid Herpetomonas ztiplika . Moreover, T. theileri was detected in three European bison, marking the first molecular confirmation of this parasite in this host. Given the absence of Leishmania DNA in both European bison and biting midges, we propose that the previous serological findings may have resulted from cross-reactivity with T. theileri rather than a true Leishmania infection.