High prevalence of Trypanosoma theileri-like trypanosomes and scarcity of monoxenous trypanosomatids in tabanids of Northwestern Russia

The hematophagous flies of the family Tabanidae are worldwide-distributed nuisance pests and at the same time vectors of various diseases for humans and livestock, including trypanosomiases.No large-scale studies dedicated to trypanosomatid infections in tabanids have been performed so far in Russia and this work intended to close this gap.Using light microscopy and molecular analyses, we screened 1180 individuals (26 species, 6 genera) of female tabanids collected in Northwestern Federal District.Our results demonstrated a high prevalence of trypanosomes (43%) belonging to the two major lineages of the Trypanosoma theileri species complex (TthI and TthII) and only a few cases of monoxenous trypanosomatids' presence.We performed statistical assessment of the obtained data and revealed differential prevalence of the two trypanosome lineages in different tabanid taxa.We also described the temporal dynamics of infections in tabanid populations: early start of trypanosome acquisition with the steady growth of overall prevalence during the season, but distinct trajectories for the prevalence of the two trypanosome haplotypes.We provided a detailed explanation of the observed results based on the available data on the biology of tabanids and proposed hypotheses concerning the reasons for distribution of trypanosomes in the peripheral blood of the ruminant hosts and trypanosome specificity.