Climate-Sensitive Redistribution of Veterinary Parasites: An Attribution Framework for One Health Surveillance and Control

Climate change is reshaping veterinary parasite transmission by altering thermal and hydrological suitability, environmental stage persistence, vector and intermediate host ecology, and contact across livestock–wildlife–companion animal interfaces. These effects are nonlinear; while warming may extend transmission in some systems, heat, desiccation, habitat loss, or disrupted hydrology can reduce the risk or concentrate transmission in local refugia. This critical narrative review compares pasture-transmitted helminths, snail-borne trematodes, environmentally transmitted protozoa, vector-borne parasites, and multi-host cycles. We propose an attribution framework that classifies observed changes across four dimensions (geographic range, seasonal timing, transmission intensity, and host-interface structure) and evaluates them through five analytical filters: suitability, parasite life-cycle response, vector or intermediate-host response, host-interface change, and surveillance artifacts. This framework prevents improved detection, land-use change, animal movement, management shifts and improved detection from being mistaken for climate-driven emergence. We also propose a climate–refugia paradox hypothesis, requiring empirical validation, in which drought or heat may reduce unselected parasite refugia and intensify selection for anthelmintic resistance. Finally, we connect a tiered diagnostic approach from field tools to reference molecular surveillance to support attribution-aware, risk-based One Health strategies that protect animal production, biodiversity, and public health.