Prävalenz pathogener Mikroorganismen bei hannoverschen Schildzecken und Vergleich mit früheren Studien

Tick borne diseases consistently represent an issue for human and animal health. Although an indispensable part of the one health-approach, long-term monitorings analysing pathogen prevalence in hard ticks are scarce. Therefore, the aim of the present study was to determine current infection rates of A. phagocytophilum, Rickettsia spp. and Borrelia spp. in I. ricinus ticks. Additionally, the study serves as a follow-up to studies conducted in 2010 and 2005, thus, statistical analysis of the development of tick infection rates with named pathogenic microorganisms was a second major aim. In the year 2015, a total of 2100 I. ricinus were collected at ten different recreational ares in the city of Hanover, Germany, and analysed by using molecular techniques. In the year 2015, a total of 3.8% of investigated ticks was infected with A. phagocytophilum. Stage-specific infection rates were 7.2% in adults (9.4% of females, 4.9% of males) and 2.4% in nymphs. Statistically significant differences were observed between stages, locations and months. Data comparison over the 10-year monitoring period revealed constant A. phagocytophilum infection rates. However, a significant increase of A. phagocytophilum positive females between 2015 (9.4%) and 2010 (0.0%) as well as 2005 (4.1%) was determined. Furthermore, adult ticks were significantly more often infected with A. phagocytophilum compared to 2010 (7.2% vs. 4.1%). While the comparison of seasonal infection rates between study years revealed significant differences, local infection rates were constant between study years. Concerning Rickettsia spp. infection rates, 50.8% of all tested ticks were positive, with an infection rate of 54.1% in adults (57.6% females, 50.5% males) and 49.5% in nymphs. Significant differences were also found between stages, locations and months. Overall, numbers of Rickettsia-positive ticks increased significantly over the course of the 10-year study period, comprising all stages. Additionally, seasonal and local differences were determined. Analyses of Borrelia spp. infection rates resulted in a total of 24.0% infected ticks, with infection rates of 35.4% in adults (38.5% females, 32.3% males) and 19.8% in nymphs. Significant differences were found between adults (females as well as males) and nymphs. Moreover, local, but no seasonal differences were found. Species differentiation was successful in 52.7% of Borrelia spp. positive ticks, with 8.9% of them identified as B. miyamotoi. Despite constant total infection rates, distribution of B. burgdorferi s.l. genospecies showed significant differences compared to previous studies. From 2010 to 2015, a significant decrease of B. afzelii and B. spielmanii was observed. In addition, in the year 2015 multiple infections were less frequent than in 2010. Concerning co-infections of Rickettsiales (A. phagocytophilum and Rickettsia spp.), a significant renewed increase between 2010 (0.6%) and 2015 (2.2%), but not compared to 2005 (2.8%) was found. In 2015, 10.9% of ticks were co-infected with Borrelia spp. and Rickettsia spp., representing a significant increase compared to 2010 (7.3%). Furthermore, coinfection rates of Borrelia spp. and A. phagocytophilum increased significantly between 2010 (0.3%) and 2015 (1.1%). Data comparison of triple-infections revealed no significant differences between study years. A continuous monitoring of tick infection rates with pathogenic microorganisms is an indispensable part of a public health risk assessment. Therefore, a follow-up monitoring starting in the year 2020 is planned.