Country-wide assessment of tick-borne pathogens collected in ticks between 2021 and 2024 in Germany, with a focus on Francisella: A one health pilot study

Ticks are important vectors for several pathogens, among which <i>Francisella tularensis</i> subsp. <i>holarctica</i> is the most relevant tularaemia-causing subspecies in Europe. The number of human tularaemia cases in Germany has increased in recent years, and ticks play an important role in disease transmission. The aim of this study was to perform a pilot study addressing the presence of tick-borne pathogens in ticks across Germany, with a special focus on <i>Francisella</i>. A total of 339 <i>Dermacentor reticulatus</i> ticks and 353 <i>Ixodes ricinus</i> ticks were collected in Germany between 2021 and 2024. DNA was extracted and analysed individually by multiplex qPCR assays detecting <i>F. tularensis</i> subsp. <i>holarctica</i>, <i>Francisella</i>-like endosymbionts, <i>Rickettsia</i> spp., <i>Borrelia burgdorferi</i> sensu lato complex, <i>B. miyamotoi</i>, <i>Anaplasma phagocytophilum</i>, <i>Ehrlichia</i> spp., <i>Coxiella burnetii</i>, <i>Bartonella</i> spp., <i>Babesia</i> spp., and tick-borne encephalitis virus. PCR testing revealed a varying frequency of these pathogens depending on the tick species. The most frequently identified bacteria were <i>Francisella-</i>like endosymbionts (18-97 %), <i>Rickettsia</i> spp. (32-74 %), and <i>B. burgdorferi</i> (0-16 %). The occurrence of <i>F. tularensis</i> subsp. <i>holarctica</i>, <i>B. miyamotoi</i>, <i>A. phagocytophilum</i>, <i>Babesia</i> spp., and tick-borne encephalitis virus was observed at a low frequency in ticks (less than 10 % in either tick species). <i>Coxiella burnetii</i>, <i>Ehrlichia</i> spp., and <i>Bartonella</i> spp. were not detected in the investigated ticks. More than 70 % of <i>D. reticulatus</i> ticks and 19 % of <i>I. ricinus</i> ticks were positive for at least two pathogens. There was a significant co-occurrence of <i>Francisella-</i>like endosymbionts and <i>Rickettsia</i> spp. in both tick species. This pilot study offers a framework for the surveillance of common, rare, and newly emerging tick-borne pathogens in Germany.