Spatial Epidemiology and Ecological Determinants of Ticks and Tick-Borne Pathogens Co-Circulation in Brijuni National Park, Croatia.

Tick-borne diseases are a growing public health concern in the Mediterranean. Brijuni National Park (BNP), a unique, highly visited island ecosystem characterized by increased large game host density and diverse Mediterranean habitats, presents an elevated risk for pathogen co-circulation. This study addresses the lack of spatial and epidemiological data to accurately assess human exposure risk in this environment. We performed a detailed geospatial and epidemiological risk mapping of pathogen co-circulation in BNP. A total of 587 hard ticks were collected across 26 georeferenced micro-locations (2020-2022). Ticks were morphologically identified and subsequently screened for six key zoonotic bacterial pathogens using qPCR. The Minimal Infection Rate (MIR) and a Co-infection Rate (CR) were calculated. Geographic Information System (GIS) mapping was utilized to map ecological determinants of risk. Ixodes ricinus was the overwhelmingly dominant vector (94.0%), peaking in spring, with activity absent in summer. Recorded diverse tick fauna also included Hyalomma marginatum (3%), Haemaphysalis punctata (2%), Ixodes frontalis (0.8%) and Rhipicephalus sanguineus (0.2%). Active circulation of Borrelia burgdorferi s.l. (Bbsl), Anaplasma phagocytophilum, and Ehrlichia canis were confirmed. Bbsl presented the highest MIR (3.05). The Co-infection Rate (CR) was notably high at 29.41%, with triple co-infections (Bbsl, A. phagocytophilum, E. canis) concentrated in cultivated mosaics and holm oak forests (Quercus ilex L.). The highest number of ticks was recovered from ecotone zones, accounting for 50.0% of the total catch, confirming them as high-risk interfaces. The absence of Rickettsia conorii may be attributed to the strict control/absence of its primary host (domestic dogs). The presence of the exotic vector H. marginatum was also confirmed. The high rate of co-infection and the spatial concentration of risk in specific habitats underscore an elevated and complex public health risk in BNP, closely linked to habitat structure and increased game host density. This research provides an essential geospatial framework for targeted 'One Health' management, prioritizing vector control in ecotone zones and dense forest refugia. Urgent surveillance for the exotic H. marginatum is warranted to monitor the potential risk of Crimean-Congo Hemorrhagic Fever.