Ticks are blood-feeding parasites which act as major vectors for various pathogenic microorganisms affecting both animal and human health. Hard ticks are known to “hitchhike” on migratory birds as they transit from breeding to overwintering grounds in spring and autumn, potentially leading to exchange and establishment of non-endemic tick species in novel environments. That said, it is not yet clear which migratory bird taxa play a role in movement of specific tick genera and what influence migratory season may have. To fill this knowledge gap, we performed a systematic literature review regarding primary data of ticks moving on migratory birds within the African-Western Palearctic flyways. In total, 34 studies were found which showed 123 bird species from 37 families connected to potential movement of 26 tick species representing six genera (Amblyomma, Dermacentor, Haemaphysalis, Hyalomma, Ixodes, Rhipicephalus). Statistical analysis showed bird families (Ixodes: Turdidae, Prunellidae; Hyalomma: Turdidae, Strigidae, Muscicapidae, Motacillidae, Emerizidae) which carried above average number of ticks were only found for interactions with Hyalomma and Ixodes ticks with below average estimates found for all tick genera besides Rhipicephalus. Contrary to expectation, no tick genus, which was found in both migratory seasons, was estimated to have increased numbers in one season or the other. In certain cases, tick genera (e.g., Amblyomma) were only found on birds during spring migration. This pattern could highlight that the assemblage of ticks present on a bird at capture does not represent the ticks present at the point of migratory departure, highlighting an understudied importance of stopover sites to potential tick introduction or turnover. Taken together, the results presented here provide guiding information for further analysis into species specific interactions which will allow for the integration of individual level variation into understanding the risk of tick movement with migratory birds and potential for emergent disease.

Lyme borreliosis (LB) is the most common vector-borne disease in the Northern Hemisphere caused by spirochetes belonging to the Borrelia burgdorferi sensu lato (Bbsl) complex. Borrelia spirochetes circulate in obligatory transmission cycles between tick vectors and different vertebrate hosts. To successfully complete this complex transmission cycle, Bbsl encode for an arsenal of proteins including the PFam54 protein family with known, or proposed, influences to reservoir host and/or vector adaptation. Even so, only fragmentary information is available regarding the naturally occurring level of variation in the PFam54 gene array and its impact on Borrelia pathogenesis. Utilizing whole genome data from isolates (n=141) originated from the three major LB-causing Borrelia species across Eurasia (B. afzelii, B. bavariensis, and B. garinii), we aimed to characterize the diversity of the PFam54 gene array in these isolates to facilitate understanding the evolution of PFam54 orthologs on an intra- and interspecies level. We found an extraordinarily high level of variation in the PFam54 gene array with 39 PFam54 paralogs belonging to 23 orthologous groups including five novel paralogs. Even so, the gene array appears to have remained fairly stable over the evolutionary history of these Borrelia species. Interestingly, genes outside Clade IV previously associated with host or, proposed, vector adaptation more frequently displayed signatures of diversifying selection. Taken together, our findings support the idea that non-Clade IV orthologs could play a larger role in host and/or vector adaptation than previously thought.