Assessing the impact of human behavior on transmission dynamics of Lassa Fever in Grand Bassa County, Liberia, from 2017 – 2028

Introduction: Lassa Fever remains a major public health problem in West Africa. Annually, 100,000 to 300,000 infections occur with approximately 5,000 deaths. In Liberia, Lassa fever outbreaks with high case fatality have been widespread despite the implementation of a national plan to curb the disease. Grand Bassa County has experienced sustained transmission since 2021. We developed a mathematical model for Lassa Fever focused on District 3A&B, Grand Bassa County to demonstrate the potential impact of intervening on behavioral transmission routes. Methods: A composite model for Lassa fever spillover risk was parameterized using routine surveillance data, detailed outbreak line lists, and Demographic and Health Survey data. The spillover model component was gender and age-stratified to capture socio-behavioral practices hypothesized by national stakeholders to enhance transmission risk among women and girls relative to men and boys. A rodent transmission model component was fit to account for differential infection among Mastomys rats inside and outside the house and seasonality in vector abundance. The impact of behavioral interventions on differential case counts between males and females was quantified. Results: Socio-demographic, clinical, epidemiological, and behavioral data on 83 confirmed Lassa fever cases (63% female) reported in line-lists between 2017 and 2022 were available for District 3A&B. The model projected a cumulative incidence of 50.9 care-seeking female cases (IQR: 35.4-76.4) and 22.7 care-seeking male cases (15.4-33.2) in District 3A&B for 2023-2027. Environmental clean-up to reduce rodent recruitment into houses led to the largest overall reductions in case counts, while safer handling practices of hunted rodent meat considerably reduced disparities in case counts. Reduced transmission via consumption of uncovered and contaminated food enhanced disparities in case counts. Conclusion: Diverse local data were used to inform a Liberia-specific model of Lassa fever. The most effective intervention as shown by the model that affected both sexes was environmental cleanup.