Genetic uniformity and occurrence of Bartonella bovis in European cattle: Indications of exophagic transmission.

Bartonella bovis is an intracellular bacterium infecting cattle, with competent vectors yet to be determined. We compared B. bovis prevalence between pasture-raised and indoor-housed cattle to assess potential vector candidates. A total of 548 blood samples from Czech cattle and 48 samples from cattle from southeastern Romania were analyzed using qPCR (ssrA gene) and nested PCR (gltA gene). In pasture herds, 18.39% (64/348) of samples were positive, all but one representing a single B. bovis genotype identical to isolates from Brazil, Guatemala, and France. In Romanian herds, also reared outdoors, prevalence was 12.5% (6/48) mostly matching Czech genotypes. These results indicate low genetic diversity of B. bovis compared to other Bartonella species (e.g., B. schoenbuchensis in red deer), supporting a clonal population structure. In contrast, indoor cattle were completely negative (0/200). The exclusive occurrence of B. bovis in pasture-raised cattle and their exposure to blood-feeding arthropods suggests transmission by exophagic vectors, possibly horn flies (Haematobia irritans) or horseflies (Tabanidae). Overall, our findings, while not demonstrating the competence of a specific vector, provide epidemiological indications that outdoor exposure supports vector-borne transmission and narrows the range of plausible candidate vectors in Europe.