Epidemiological and Molecular Analysis of Lassa Mammarenavirus in Mastomys Rodent Reservoirs in Ondo and Edo States

Lassa fever transmission in Nigeria is driven by the multimammate rat Mastomys natalensis, which chronically sheds Lassa mammarenavirus in urine and faeces in and around human habitations. Understanding the spatial density of Mastomys populations and their viral carriage rates is critical to predicting human Lassa fever risk. This study characterises the prevalence and molecular diversity of Lassa mammarenavirus in Mastomys populations across high-burden communities in Ondo and Edo states, South West and South South Nigeria. Mastomys rats will be trapped using Sherman live traps at 30 peri-domestic sites across six local government areas over two trapping seasons (dry and wet). Kidney, lung, and liver tissues will be collected for Lassa virus RNA extraction and RT-PCR. Positive samples will undergo full-length S segment sequencing for phylogenetic analysis. Concurrent environmental data on rodent contact risk factors (food storage practices, household structure type) will be collected from householders at each site. Prior studies from Ondo State identified multiple Lassa virus lineages in Mastomys, suggesting ongoing within-host evolution. A combined ecological and molecular approach fills critical gaps in understanding reservoir-to-human transmission corridors. Findings will inform spatially targeted rodent control interventions and contribute molecular data to the global Lassa virus phylogenetic framework under the WHO Research and Development Blueprint. Keywords: Lassa mammarenavirus, Mastomys natalensis, reservoir, molecular analysis, Ondo State