PCR screening of 1,482 murid rodents from 13 genera caught in 18 different localities of Guinea, West Africa, showed Lassa virus infection only in molecularly typed Mastomys natalensis. Distribution of this rodent and relative abundance compared with M. erythroleucus correlates geographically with Lassa virus seroprevalence in humans.

Based on empiric surveillance data, the incidence of human Lassa fever (LF) cases in Guinea and other West African countries has been reported to increase during the dry season compared to the rainy season. To investigate possible links with the ecology of the rodent reservoir of the virus, we conducted a 2-year longitudinal survey of Mastomys natalensis in a region of high human Lassa virus (LASV) seropositivity in Guinea. Standardized rodent trapping with similar trapping efforts between seasons was performed in three villages and 53.5% (601/1123) of the animals were identified as M. natalensis using morphometric and molecular criteria. Mean trapping success (TS) of M. natalensis was always higher inside houses than in proximal cultivations. In the dry season, mean TS increased 2-fold inside houses and decreased up to 10-fold outside (p < 0.0001), suggesting aggregation of rodents inside houses due to restricted food supply. 14.5% (80/553) of M. natalensis were tested positive for Lassa virus by reverse transcription-polymerase chain reaction (RT-PCR; range, 5%-30%) and prevalence of the virus was two to three times higher in rodents captured in the rainy season than in the dry season (p < 0.05). Inside houses, however, the LASV prevalence fluctuated nonsignificantly with season. These data suggest that in Guinea the risk of LASV transmission from rodents to humans is present both in the rainy and the dry season, reflected by the occurrence of LF cases throughout the year. In the dry season, however, the increased risk of humans encountering Mastomys and their excreta inside of houses may result in an increase of human Lassa fever cases.

We recently discovered a novel hantavirus, Sangassou virus, in Guinea, West Africa. Using enzyme-linked immunosorbent assays followed by confirmatory and serotyping assays, we retrospectively detected hantavirus antibodies in 3 (4.4%) of 68 patients with fever of unknown origin in Sangassou village, Forest Guinea. A population-based survey in Forest Guinea (n = 649) found the prevalence of hantavirus antibodies to be 1.2%. Specific neutralizing antibodies against Sangassou virus were demonstrated in serum samples from 2 patients and in 2 serum samples of the serosurvey. Our data allow us to conclude that hantavirus infections may be a significant unrecognized medical problem in at least this part of Africa.

We compiled the first taxonomic inventory of rodents inhabiting the region from northwestern Guinea to coastal Guinea and this enabled an improved understanding of the rodent fauna of this unexplored region at the western margin of the guineo-congolese forest block. Through standard cytogenetic and morphological analyses we described the presence of two sibling species of the genus Mastomys in West Africa. We report here the first records for Guinea of Arvicanthis ansorgei and M. mattheyi. Our data indicated an extension of the known distribution of Lemniscomys striatus to include the western region of the range of Lophuromys cf. sikapusi. A comparison between southern Senegal, southern Mali, Ivory Coast and eastern Guinea assemblages shows some differences in the rodents between eastern and western Guinea as well as with the surrounding countries. It appears that coastal Guinea could correspond to a transition zone between forest and savanna but this region appears to be ecologically highly degraded in terms of its small mammal communities. Rattus rattus is found in all sampled localities but Mus musculus is restricted to one locality where it was the dominant species of the assemblage. Our study highlights the importance of surveys of rodent biodiversity in unexplored zones.

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