In a survey of rodentborne hemorrhagic fever viruses, 1,591 small mammals were trapped in Guinea from 2002 to 2005. Total RNA was extracted from rodent blood preserved in liquid nitrogen by using the Blood RNA kit (Peqlab, Erlangen, Germany). A 1-step RT-PCR targeting a highly conserved region of the RNA polymerase (L) gene was performed by using primers LVL3359A-plus (5´-AGAATTAGTGAAAGGGAGAGCAATTC), LVL3359D-plus (5´-AGAATC
AGCAATTC), LVL3359G-plus (5´-AGAATTAGTGAAAGGGAGAGT
TC), LVL3754A-minus (5´-CACATCATTGGTCCCCATTTACTATGATC), and LVL3754D-minus (5´-CACATCATTGGTCCCCATTTACTG
TGATC) (Note: Underlined letters represent differences in nucleotides among plus and minus primers). Because Lassa virus antigen should be frequently detectable in the natural host, and specific antibodies are known to be negatively correlated with its presence, they were not investigated in this study (9
The animals were caught in 18 different study sites representative of the principal geographic regions of Guinea (10
) (). All sites were rural villages with a population <
1,000. Human Lassa fever seroprevalence was previously reported to be low (0%–11%) in 6 trapping areas and high (25%–55%) in 12 trapping areas (11
, ). Of 1,482 murid rodents belonging to 13 genera and at least 20 species, we typed 847 as M. natalensis and 202 as M. erythroleucus but none as M. huberti, by using DNA from liver biopsies. In addition, we karyotyped 12 members of the genus Mastomys in the field by using standard procedures (14
Figure 1 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 (more ...)
We obtained positive RT-PCR results from 98 (1.2%) of 1,482 murid rodents. Sequence analysis showed 96 Lassa virus strains with 96%–100% amino acid homology with the prototypic strain Josiah. Lassa virus–positive rodents were only captured in the prefectures of Faranah (villages of Gbetaya, Bantou, Tanganya) and Guéckédou (Denguédou), both situated along the border with Sierra Leone (). We PCR-typed all Lassa virus–positive rodents unequivocally as M. natalensis, with 1 male (no. BA686) additionally confirmed by karyotyping (2n = 32, autosomal fundamental number = 53). Overall, 11.3% of M. natalensis were infected with Lassa virus (), with 0% in the low seroprevalence area and 5.4%–32.1% in the Lassa fever high seroprevalence area. In the coastal region, where the lowest human Lassa virus seroprevalence (0%–6%) has been reported, only M. erythroleucus was captured. In contrast, in the forest region, where the highest seroprevalence of up to 55% in selected villages has been found, only M. natalensis was trapped (11
). Both species were captured in the savannah regions, where seroprevalence was 2%–42%, but M. natalensis was captured more frequently ().
Small mammal species examined for arenavirus infection by reverse transcription PCR*
Lassa virus was isolated in cell culture from 32 rodents, and a 631-bp fragment of the nucleoprotein gene previously used for phylogenetic analysis was sequenced (GenBank accession nos. DQ832667–DQ832699) (15
). The phylogenetic tree shows that all isolates belong to the lineage IV of Lassa virus and that strains from the prefecture of Faranah cluster with strains isolated previously from human patients of the same region (15
) (). We detected 2 novel L-gene sequences that shared 68%–74% homology with lymphocytic choriomeningitis virus in 2 rodents of the Mus subgenus Nannomys.
Figure 2 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% (more ...)