Understanding Lassa fever through a one health lens: How climate, land use, and poverty shape transmission in Nigeria

Lassa fever (LF) is a zoonotic viral hemorrhagic disease endemic in West Africa, whose outbreaks are increasingly shaped by environmental and socio-ecological changes. Understanding these drivers within a One Health framework is critical for predictive control. This study has systematically identified and synthesized evidence on climatic, ecological, and socio-environmental determinants of Lassa fever transmission in Nigeria. Following PRISMA 2020 standards and a PROSPERO-registered protocol (CRD420251139166), we searched PubMed, Scopus, Web of Science, Google Scholar, and AJOL for studies published between 2000 and 2025. Eligible studies examined climatic, ecological, or socio-environmental determinants of LF in humans or rodent reservoirs. Quality appraisal used JBI, NOS, and PROBAST tools. Due to methodological heterogeneity, results were narratively synthesized. Of 445 records screened, 57 studies were included. Our synthesis identified three key findings. Socio-environmental factors particularly poor housing (aOR = 1.94) and unsafe food storage were the most consistent and proximal drivers of human risk. Climatic drivers, especially lagged rainfall (e.g., +0.62 % increase in the reproduction number R 0 per 1 mm rainfall at 7-month lag), robustly predicted seasonal outbreaks. Ecological changes like agricultural expansion and urbanization (OR = 23.3) increased spillover risk, whereas greater rodent biodiversity was associated with lower risk (OR = 0.85), suggesting a potential 'dilution effect' that requires further validation. Lassa fever transmission in Nigeria arises from interacting climatic, ecological, and socio-economic conditions. Integrated One Health surveillance combining environmental data, rodent ecology, and social determinants is essential for early warning and sustainable outbreak control. • Socio-environmental vulnerabilities are key drivers of human infection, with poor housing and unsafe food storage creating rodent-human interfaces. • Climatic factors, particularly lagged rainfall, robustly predict seasonal outbreaks. • Anthropogenic landscape changes elevate spillover risk, as agricultural expansion and urbanization increase human-rodent contact. • A pervasive knowledge-practice gap undermines prevention; despite high community awareness (>80 %). • Transmission follows a predictable syndemic cascade requiring integrated One Health interventions.