Abstract
Lassa virus (LASV) outbreaks in West Africa pose a significant public health threat. We investigated the infection phenotype and transmission (horizontal and vertical) of LASV strain Ba366 in its natural host, Mastomys natalensis. Viral RNA levels in body fluids, virus titers in organs and antibody presence in blood were analyzed. In adults and 2-week-old animals, LASV caused transient infections with subsequent seroconversion. However, neonates and younger juveniles exhibited persistent infections lasting up to 16 months despite antibody presence. LASV was detected in various body fluids, organs, and cell types, primarily in lung, kidney, and gonadal epithelial cells. Despite the systemic virus presence, no pathological alterations in organs were observed. Infected individuals efficiently transmitted the virus throughout their lives. Our findings underscore the crucial role of persistently infected individuals, particularly infected females and their progeny, in LASV dissemination within the host population.