Map of Guinea showing the location of the 18 trapping sites (small circles). Sites where only Mastomys erythroleucus or M. natalensis were trapped are shaded in gray and black, respectively. Sites where both species were captured are hatched, and sites where no Mastomys were caught are marked with a dash. The human Lassa virus seroprevalence in these areas is indicated by the size of the sectors of the larger circles shaded black (), gray (), or hatched (). The asterisk denotes the Madina Oula refugee camp on the border with Sierra Leone, where human seroprevalence was high (), with 23% of the Mastomys Lassa virus antigen or antibody positive (). In close localities, no Lassa virus–positive Mastomys were found ().

Phylogenetic relationships of Lassa virus strains based on a nucleoprotein gene fragment (631 bp) determined by using the neighbor-joining method. The numbers above branches are bootstrap values >50% (1,000 replicates). Scale bar indicates 10% divergence. Localities are indicated by the specimen label: DGD (Denguédou), BA (Bantou), GB (Gbetaya), and TA (Tanganya).