Vectorial dynamics underpinning current and future tick-borne virus emergence in Europe

Abstract

Tick-borne diseases pose a growing threat to human and animal health in Europe, with tick-borne encephalitis virus (TBEV) and Crimean-Congo haemorrhagic fever virus (CCHFV), vectored by Ixodes ricinus and Hyalomma marginatum, respectively, emerging as primary public health concerns. The ability of ticks to transmit pathogens to multiple hosts and maintain infections across life stages makes them highly efficient vectors. However, many aspects of tick ecology and vectorial capacity remain understudied. This review examines key factors contributing to the vectorial competence of European ticks and their associated viruses. We first explore the influence of climate change on vector and disease ecology, using TBEV and CCHFV as case studies. We then analyse the role of the tick antiviral response in shaping vector competence. By integrating these elements, this review aims to enhance our understanding of tick-borne viral diseases and support the development of public health strategies, particularly through the One Health framework, to mitigate their impact in Europe.

Keywords: climate change; emerging viruses; tick immunity; tick-borne diseases; vector competency.

Fig. 1.. Transmission dynamics of TBEV between ticks and reservoir hosts. Vertical transmission through transstadial and transovarial transmission is shown in green. Horizontal transmission between the tick and vertebrate hosts is shown in red.

Fig. 2.. Current and future distribution of the main tick vector species in Europe. Distribution of I. ricinus, H. marginatum and D. reticulatus ticks in Europe, as of October 2023. Regions where the species is present are shown in red. Predicted introduction regions are in pink, while observed introduction regions are in yellow. Light blue indicates regions where the species is anticipated to be absent, blue where the species is observed absent, and dark blue represents regions with predicted absence. Adapted from the ECDC and European Food Safety Authority, 2023. SSP370 predictions for I. ricinus and D. reticulatus were adapted from Cunze et al. [163], and H. marginatum adapted from Hekimoglu et al. [61].

Fig. 3.. Representation of environmental, biological and human factors impacting tick-borne viral disease emergence. Adapted from Lindgren [58]. Each arrow represents identified drivers, facilitating different categories of impact, which are ranked from the most determinants to the least (adapted from [66]). Created in BioRender.

Fig. 4.. Innate immune pathways of the main European tick vectors, Ixodes spp. and Hyalomma spp. Schematic representation of the JAK-STAT (orange), Imd (green), Toll (blue) and c-Jun N-terminal kinase (yellow) pathways adapted from [125] for Hyalomma spp. and for Ixodes spp. [9293 103 126]. Plain coloured proteins are known factors, dashed grey proteins represent non-identified proteins. Created in BioRender.