Lassa Virus Persistence with High Viral Titers Following Experimental Infection in Its Natural Reservoir Host, Mastomys Natalensis

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. Here we analyze viral RNA levels in body fluids, virus titers in organs and antibody presence in blood. In adults and 2-week-old animals, LASV causes transient infections with subsequent seroconversion. However, mice younger than two weeks exhibit persistent infections lasting up to 16 months despite antibody presence. LASV can be 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 are observed. Infected animals efficiently transmit 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. Mastomys natalensis, a mouse found closely to rural human dwellings in Sub-Saharan Africa, is a major reservoir for Lassa Virus (LASV). Here, the authors show that LASV causes transient infections in adult M. natalensis, but persistent infections in young animals despite antibodies. LASV is found in various organs without causing pathology and infected animals efficiently transmit the virus.