One health perspectives on Lassa fever: a systematic review of human, animal, and environmental risk factors in endemic areas of Nigeria

Lassa fever is a zoonotic viral haemorrhagic disease caused by Lassa virus (LASV), endemic across multiple states of Nigeria and responsible for approximately 70% of the global burden. Annual outbreaks cause thousands of deaths, yet persistent transmission indicates that the complex interplay of human, animal, and environmental risk factors remains incompletely understood. Applying a One Health framework offers a more integrated approach for understanding and interrupting transmission across these interconnected domains [1]. We conducted a systematic review following PRISMA 2020 guidelines. Five databases were searched (PubMed, Scopus, Web of Science, AJOL, and Google Scholar), supplemented by grey literature. Studies published between January 2000 and March 2025 were eligible if they investigated at least one domain of Lassa fever risk within Nigerian endemic areas and contained empirical data. Quality appraisal used CASP and JBI checklists. Data were synthesised thematically. The review protocol was registered with PROSPERO (registration number: CRD420261436085; available from: https://www.crd.york.ac.uk/PROSPERO/view/CRD420261436085 ). Of 612 records identified, 38 studies met eligibility criteria. Human risk factors — including open food storage, occupational exposure, poor household hygiene, and nosocomial transmission in facilities without adequate IPC — were the most consistently reported determinants. Animal risk factors centred on the peri-domestic ecology of Mastomys natalensis, with rodent density strongly correlated with human exposure. Environmental determinants — poor housing, inadequate waste management, deforestation, climate variability, and peri-urban expansion — were identified as contextual amplifiers. Spatial analyses confirmed perennial hotspots in Edo, Ondo, Ebonyi, and Plateau states, with seasonal peaks at the end of the rainy season. Lassa fever endemicity in Nigeria is sustained by converging human, animal, and environmental determinants. Effective control requires an integrated One Health strategy encompassing strengthened IPC and diagnostics, community-based rodent-proofing and sanitation programmes, coordinated human–animal–environment surveillance, culturally tailored risk communication, and sustained domestic financing.