Impact of extreme weather events on tick-host dynamics and disease risk in mountainous regions: the study case of Vaia windstorm in the north-eastern Italian Alps

In 2018, the windstorm ‘Vaia’ hit the North-Eastern Italian Alps causing the loss of 42 million trees across over 42500 hectares by creating fragmented habitats that alter local animal communities and raise disease risk concerns. The area is part of the BEPREP project focusing on biodiversity recovery to reduce disease spread. This study evaluates the responses of hosts to a catastrophic event in terms of community composition and relative abundance and the consequences on zoonotic risk using small mammals, ticks and tick-borne pathogens as a model system. The study site is located in the Paneveggio-Pale di San Martino Natural Park (Autonomous Province of Trento, Northern Italy). Twelve sites are identified in three different habitat types (post-Vaia windthrow, forest and meadow), both at 1100 and 1700 m a.s.l. In each site, we performed Capture-Mark-Recapture live-trapping of small mammals and tick-dragging along transects during 2023/2024. Bacteria and protozoa were detected in ticks using PCR-based methods combined with sequencing. In total 212 Ixodes sp. ticks were collected through transects (97 in 2023 and 115 in 2024), with a higher tick density in Vaia sites compared to forest ones. Tick-borne pathogens screening of ticks collected in 2023 (for 2024 analyses are ongoing) reported Anaplasma phagocytophilum (3.33%), Babesia venatorum (5%), Rickettsia monacensis (3.33%) and Borrelia afzelii (20%) in Vaia sites, while in the forest only B. afzelii (16.22%) and B. burgdorferi s.s. (5.41%) were detected. We captured 261 small mammal individuals belonging to Apodemus flavicollis, A. sylvaticus, Clethrionomys glareolus, Microtus spp. and Sorex spp. Small mammal diversity was higher in Vaia sites. Vaia sites are undergoing natural reforestation, with heterogeneous habitats that promote the interface between vectors and hosts, raising disease risk. This study emphasizes understanding habitat changes' ecological effects on animal communities and disease transmission.