Defining One Health: Environment versus ecosystem.

BACKGROUND: This article seeks greater precision in defining One Health by clarifying ambiguities and elaborating issues that arise from the One Health High-Level Expert Panel (OHHLEP) definition, while acknowledging the utility of the OHHLEP definition and the consensus it represents. In particular, we clarify certain implications of how the third, environmental component of One Health is understood. METHODS: We developed our argument by taking part in the interdisciplinary Science Advice for Policy by European Academies (SAPEA) consortium for One Health Governance in the European Union. We are a highly interdisciplinary team that has developed this theoretical position by meeting throughout 2024 to write the report chapter on which it is based. RESULTS: We suggest that whereas an "environment" implies something external (and perhaps subordinate) to humans and animals, an "ecosystem" implies a system of which both humans and animals are part (alongside plants, chemicals, microbes, etc.). We explore three sets of concepts within the OHHLEP definition: "integrated" and "unifying"; "balanced" and "optimised"; "closely linked"; and "interdependent." Lastly, we explain our synergies and complementarity with adjacent concepts including "Planetary Health". CONCLUSIONS: To us, clarity in these nuances seems key in the development of One Health away from an anthropocentric framing towards a more integrated and balanced framing. While we argue that the ecosystemic, holistic view is preferable and better aligned with One Health's expanding scope, we note that conditions for making practical changes are not yet able to accommodate holism.