Taking into account the spatial heterogeneity of agricultural landscapes to explain densities and movements of Ixodes ricinus and prevalence of its associated pathogens
Résumé
While most studies on Ixodes ricinus to date have focused on forest habitats, the main European tick species is also widely found in agricultural landscapes including pastures, hedgerows and small woods. Because wildlife and domestic fauna share these habitats and are both feeding hosts for ticks and reservoirs for numerous tick-borne infectious agents, understanding of the epidemiology of associated diseases must explicitly take into account the spatial arrangement of these different biotopes. During the OSCAR project (https://www6.inra.fr/oscar/), we have investigated two comparable agricultural landscapes located in France to analyse the potential importance of this landscape interface on Anaplasma phagocytophilum, Borrelia spp. and Babesia spp. prevalence. In the ecotones between pastures and wooded areas, tick density was linked to wood mouse abundance (Apodemus sylvaticus) the previous year. The A. phagocytophilum prevalence was higher in roe deer (75%) than in rodents (6.9%) or in tick nymphs sampled on the vegetation (1.9%), with density of cattle being positively linked to this last prevalence. Using both SNP and microsatellite genotyping of individual ticks, extensive gene flow was reported among landscape components within each study site probably linked to tick dispersal via host movements. Indeed, GPS analyses of collared roe deer revealed the use of almost all landscape components by these tick hosts. Finally, a landscape simulator was built, and based on information from a model explaining tick density in relation to different landscape features, tick density was mapped on simulated landscapes allowing to investigate how land use changes affect tick density.