Human pathogemic Rickettsia from Hyalomma ticks in Germany
Background: Hyalomma marginatum and Hyalomma rufipes are two-host tick species, which are mainly distributed in southern Europe, Africa to central Asia, but may also be found in Central and Northern Europe through introduction by migratory birds.  Methods: Ticks were collected while feeding or crawling on animals and humans, or from the environment, in different regions in Germany, between 2019 to 2021 in a citizen science study and from 2022 to 2023 in the wake of this study.  Results: From 2019 to 2023, a total of 212 Hyalomma adult ticks were detected in Germany. This included 132 H. marginatum and 43 H. rufipes ticks sent to research institutions and 37 photographic records that were only identified to genus level. The number of detected ticks varied over the years, with the highest number of 119 specimens recorded in 2019, followed by 57 in 2020. Most of the specimens were collected from horses, while some were collected from other animals, humans or found crawling on human clothes or other objects inside or outside houses. The screening of 175 specimens for Crimean-Congo hemorrhagic fever virus and of 132 specimens for Babesia/Theileria spp. by PCR gave negative results, while human-pathogenic Rickettsia were detected in 44% (77/175) of the total samples. Subsequent amplicon sequencing and phylogenetic analysis of representative samples determined the species of 41 isolates as R. aeschlimannii and one R. slovaca isolate.  Conclusions: Analysis of climatic factors indicated a significant higher probability of Hyalomma occurrence at locations with higher average spring temperature during the years 2019 and 2020 when compared to randomly generated pseudo-absence locations. Dry and hot conditions probably facilitated Hyalomma nymphs' survival and molting into adults during these years.