Serological evidence of Lassa virus in commensal rodents from Senegal

Lassa fever, a neglected zoonotic hemorrhagic disease caused by Lassa virus (LASV) and endemic in West Africa, remains a significant public health concern associated with rodent exposure. Senegal lies at the western fringe of the LASV area, but only one 1988 serosurvey reported low antibody prevalence. Given recent ecological shifts, including the expansion of invasive Rattus rattus and Mus musculus, we reassessed LASV exposure in rodents from Senegal.

We retrospectively analyzed 618 archived rodent sera collected in 2012-2013 from domestic and peri-domestic environments in central and eastern Senegal. Samples were screened for LASV-specific IgG by ELISA, and IgM was assessed descriptively in IgG-positive or equivocal specimens, with cautious interpretation because rodent validation for IgM remains limited. Spatial mapping and ecological analysis identified seropositivity clusters and potential environmental correlates.

Eleven rodents were IgG-seroreactive (1.8%; 95% CI: 0.9-3.2%), and no IgM reactivity was detected, although IgM results were interpreted cautiously because rodent validation remains limited. All seroreactive animals belonged to the commensal species Rattus rattus (9/180; 5%) and Mus musculus (2/174; 1.1%) and were clustered in five villages along major transport corridors. At the locality level, overall positivity ranged from 3.3% to 28.6%, with the highest values observed in Didé Gassama (26.3%) and Kounkane (28.6%), indicating a focal rather than diffuse pattern of LASV exposure.

This study provides the first update in over three decades on LASV exposure in Senegalese rodents. IgG seroreactivity confined to invasive commensal species suggests localized exposure patterns that warrant further investigation, while the weak, non-significant association between rodent diversity and seropositivity does not support a clear diversity effect. Spatial clustering of seropositive rodents along major transport routes points to low-level but persistent circulation in settings favoring human-rodent contact. These findings provide a retrospective baseline of LASV seroreactivity in Senegalese rodents and highlight the need to integrate rodent surveillance into One Health frameworks to strengthen early warning and regional preparedness.

Not applicable.