Serosurveillance Identifies an Endemic Hotspot of Lassa Fever in Faranah, Upper Guinea

Abstract

Background: Lassa fever, caused by Lassa virus (LASV), is a rodent-borne disease endemic to West Africa. Despite growing interest from the global health community, the overall disease burden remains poorly understood due to persistent underreporting and inadequate diagnostic capacities. This study aimed to assess LASV infection dynamics in rural Guinea, addressing gaps in understanding its epidemiology in endemic settings.

Methods: A cross-sectional serosurveillance study was conducted across 6 villages in Faranah, Guinea, involving 1306 participants. Serum samples were analyzed for LASV-specific antibodies using enzyme-linked immunosorbent assay, and a subset confirmed via immunofluorescence and neutralization assays. Statistical and mathematical models were used to estimate key epidemiological parameters, including the force of infection, antibody waning rates, and infection prevalence.

Results: Overall, IgG seroprevalence was 82.3%, while IgM prevalence stood at 1.8%. Seroprevalence of IgG exceeded 50% by age 5 and increased steadily with age, indicating lifelong exposure. Antibody waning rates suggested an average IgG persistence of 58 years. Mathematical analysis showed that halving LASV prevalence would require a 10-fold reduction in the force of spillover, highlighting the challenges of effective control measures.

Conclusions: The seroprevalence observed in this study was markedly higher than reported elsewhere in West Africa, identifying Faranah as a hotspot for LASV transmission. Despite the high seroprevalence and estimated force of infection, the number of reported acute cases is very low, suggesting that LASV may frequently cause pauci- or asymptomatic infections or be commonly misdiagnosed for other diseases. These findings underscore that LASV is more widespread than assumed in rural Guinea.

Keywords: Lassa IgG; Mastomys natalensis; West Africa; force of infection; seroreversion; spillover reduction.