Scaling Up Wildlife Health Surveillance: Lessons from the Transition of Focal Marsh Deer (Blastocerus dichotomus) Mortality Monitoring to Integrated Surveillance in Protected Areas of Argentina.

Landscapes of the Anthropocene, increasingly shaped by deforestation, climate change, and productive activities, are key settings for pathogen emergence and re-emergence. In this context, wildlife health surveillance is critical for early detection and risk mitigation. We describe the development, implementation, and operational outcomes of an integrated wildlife health surveillance system in protected areas of Argentina between 2022 and 2025, following its transition from marsh deer (Blastocerus dichotomus) mortality monitoring to a multispecies framework. The system integrated participatory, passive, and active surveillance modalities, with participatory surveillance functioning as a cross-cutting component supporting both mortality event detection and field implementation. The participatory network involved 110 members and was strengthened through training, standardized protocols, and field-based collaboration. Passive surveillance documented 205 records of wildlife morbidity and mortality, structured through three complementary reporting channels: surveillance network reports, wildlife rescue centers, and research team detections. Active surveillance focused on Ehrlichia chaffeensis and Theileria cervi, combining standardized grid-based sampling with complementary sampling of domestic dogs and environmental matrices. Grid-based sampling integrated rodent trapping, tick dragging, and camera trapping within a unified spatial design, yielding 471 rodents, 696 questing ticks, and records of 14 mammal species. Additional components included 185 domestic dogs sampled in one peri-protected area and 263 environmental samples across multiple matrices. System performance varied across implementation contexts, shaped by territorial presence of personnel, local infrastructure, and continuity of field activities. Integration of surveillance modalities enabled coordinated workflows, strengthened interinstitutional collaboration, and improved sample use efficiency across concurrent research efforts, expanding detection capacity, enhancing sample quality, and reducing redundant animal handling. The diagnostic network incorporated 12 institutions supporting coordinated sample processing. This study provides an operational framework for integrated wildlife health surveillance in resource-limited settings, highlighting the role of participatory approaches and the importance of institutional support, local capacity, and sustained engagement for long-term sustainability and consolidation of existing surveillance programs under a One Health perspective.