Systematic review of environmental factors associated with severe fever with thrombocytopenia syndrome occurrences.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne viral disease with a high fatality rate among older adults. It is posing a growing public health threat across Asia, with increasing potential for geographic spread beyond the region. Control efforts remain largely confined to individual-level tick-bite prevention, reflecting persistent gaps in understanding the ecological mechanisms that sustain SFTS transmission, particularly how environmental factors shape transmission dynamics across vectors, animal reservoirs, and human populations. We systematically reviewed 2910 studies to synthesize evidence on associations between environmental factors and SFTS occurrences across populations. Temperature, humidity, precipitation, elevation, and land cover are consistently linked to human SFTS occurrence through nonlinear, often reverse-U-shaped, relationships, underscoring the need for analytical frameworks capable of capturing the inherently nonlinear nature of environmental influences. However, we identified no quantitative assessments of how environmental factors shape SFTS occurrence in vectors or animal reservoirs, nor any stage-specific assessment of how these factors act across the transmission cycle, leaving multifaceted environmental effects acting across the tick-animal-human interface collapsed into oversimplified estimates based solely on human cases. To address these critical gaps, research must prioritize stage-specific elucidation of environmental drivers across the SFTS transmission cycle through mechanistic modeling approaches integrated with transboundary surveillance under a One Health framework. As climate and land-use changes continue to reshape vector habitats and expand regions at risk, such efforts will be essential for enhancing ecological understanding and guiding One Health-grounded surveillance and control strategies that can mitigate the growing transboundary burden of SFTS.