The Prevalence of in Hard Ticks in Europe and Their Role in Q Fever Transmission Revisited-A Systematic Review.

The zoonosis Q fever is caused by the obligate intracellular bacterium . Besides the main transmission route inhalation of contaminated aerosols, ticks are discussed as vectors since the first isolation of the pathogen from a tick. The rare detection of in ticks and the difficult differentiation of from -like endosymbionts (CLEs) are questioning the relevance of ticks in the epidemiology of Q fever. In this review, literature databases were systematically searched for recent prevalence studies concerning in ticks in Europe and experimental studies evaluating the vector competence of tick species. A total of 72 prevalence studies were included and evaluated regarding DNA detection methods and collection methods, country, and tested tick species. Specimens of more than 25 different tick species were collected in 23 European countries. Overall, an average prevalence of 4.8% was determined. However, in half of the studies, no -DNA was detected. In Southern European countries, a significantly higher prevalence was observed, possibly related to the abundance of different tick species here, namely spp. and spp. In comparison, a similar proportion of studies used ticks sampled by flagging and dragging or tick collection from animals, under 30% of the total tick samples derived from the latter. There was no significant difference in the various target genes used for the molecular test. In most of the studies, no distinction was made between and CLEs. The application of specific detection methods and the confirmation of positive results are crucial to determine the role of ticks in Q fever transmission. Only two studies were available, which assessed the vector competence of ticks for in the last 20 years, demonstrating the need for further research.