Spatial distribution of commensal rodents in regions with high and low Lassa fever prevalence in Guinea

Lassa fever is a hemorrhagic fever caused by all arenavirus, which affects approximately 150,000 persons per year in West Africa. It is principally transmitted by rodents of the genus Mastomys, which serve as both reservoir and vector of the virus. This study tested the hypothesis that human Lassa fever in Guinea is related to the occurrence rate of the multimammate rat, Mastomys spp, inside houses. The analysis was based both on Lassa virus antibody surveys in the human Population and the commensal rodent distribution in the same prefectures. The analysis took into account several data sets compiled from the literature (Lukashevich et al., 1993; Demby et al., 2001) and data from Our own ongoing rodent trapping activities in Guinea. The analysis revealed a probable regional gradient of introduced rodent species in houses, with the black rat, Rattus rattus, predominating on the coast and the house mouse, Mus musculus, predominating approximately 200 kin southeast to the coast. The autochthonous species, Mastomys spp, were present deep inside the Country, from High to Forest Guinea. The regression analysis of Mastomys occurrence on human Lassa virus antibody prevalence showed a positive correlation in six administrative regional districts (prefectures) between an increasing Mastomys occurrence and increasing seroprevalence. A seventh prefecture, where mainly M. musculus occurred, was discordant with this trend, and possible explanations for this divergence are discussed. The partial replacement of Mastomys by other species, especially R. rattus and Myomys daltoni, is discussed as a potential explanation for the low-prevalence of Lassa fever in certain areas.