Tick-borne bacterial and protozoal pathogens in horses in Austria - A cross-sectional study on current and past infections and potential risk factors.

Tick-borne bacterial and protozoal pathogens are a major threat to equine health worldwide. In Austria, studies on pathogens such as piroplasms, Anaplasma phagocytophilum and Borrelia spp. in horses are scarce and do not cover the countrywide horse population. To address this, blood samples from horses without prior record of infection with tick-borne pathogens (n = 588) were tested for the presence of Theileria equi, Babesia caballi or A. phagocytophilum DNA by PCR and for specific antibodies against these pathogens and Borrelia burgdorferi with commercially available assays. While no DNA of B. caballi could be amplified, specific anti-B. caballi antibodies were detected in eleven horses (1.9% by ELISA). DNA of T. equi was amplified in twelve horses. In two horses DNA of Babesia canis was detected. Anti-T. equi antibodies were detected in the T. equi PCR-positive horses and one of the B. canis-PCR-positive animals. No A. phagocytophilum-DNA could be amplified, while anti-Ap antibodies were detected in 42.7% (IFAT) resp. 57.3% (ELISA) of 544 horses, and 44.2% had specific anti-B. burgdorferi antibodies. Of the A. phagocytophilum-seropositive horses, 57.8% were also positive for B. burgdorferi. In total, 28% of the horses were positive for two or three pathogens. Common significant associations with infections included pasturing and housing, and, for T. equi, also place of birth/import. High infection rates with A. phagocytophilum and B. burgdorferi indicate a significant exposure of Austrian horses for ticks and tickborne pathogens in general, and, together with the T. equi infections detected throughout the country, highlight the potential risk of transmission to vectors with further infections of horses and subsequent disease after tick bites during pasturing or outdoor activities, and should alert veterinarians to include these etiologies as differential diagnoses in clinically overt cases.