Fluctuation of Abundance and Lassa Virus Prevalence in Mastomys natalensis in Guinea, West Africa

Abstract

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.

New data on the taxonomy and distribution of Rodentia (Mammalia) from the western and coastal regions of Guinea West Africa

“…In Mali, Granjon et al (2005b) found M. huberti in the inner delta of Niger and in south Mali and it is known in wet zones of S. Senegal . From our previous works in North East Guinea and Central Guinea, M. natalensis and M. erythroleucus are recorded in the same villages but never M. huberti (Denys et al 2005b;Lecompte et al 2006;Fichet-Calvet et al 2007). In the Nimba region, Gautun et al (1986) described two morphs but failed to attribute them and no karyotypes were Figure 12.…”

Lassa Fever 2016 Outbreak in Plateau State, Nigeria—The Changing Epidemiology and Clinical Presentation

“…However, we also found the occurrence of LF in August indicating that infection potentially can occur at any time of the year. Similarly, in Guinea, as in other West African countries, LF is known to occur throughout the year but is more common in the dry season due to higher numbers of M. natalensis in homes due to restricted food supply (22). …”

Rat-atouille: A Mixed Method Study to Characterize Rodent Hunting and Consumption in the Context of Lassa Fever

“…The significance of these contacts in terms of LASV transmission depends on their frequency and on the proportion of M. natalensis in the catch, i.e., on the number of M. natalensis caught and eaten. Ecological studies in Guinea suggest that M. natalensis is predominantly found in houses and proximal cultivations, but infrequently in distal cultivations (Fichet-Calvet et al 2007), thus consumption of M. natalensis might be less important relative to other rodents. The potential in variation to LASV exposure along a geographically induced behavioral gradient (consumption of bush rats vs. non-consumption of town rats), as well as preference and avoidance of certain species, provides a strong argument to investigate human behaviors as drivers for disease emergence (Kock 2014) and their overlay with the eco-epidemiology of zoonotic diseases and reservoir species.…”