Lassa virus (LASV) causes a deadly haemorrhagic fever in humans, killing several thousand people in West Africa annually. For 40 years, the Natal multimammate rat, Mastomys natalensis, has been assumed to be the sole host of LASV. We found evidence that LASV is also hosted by other rodent species: the African wood mouse Hylomyscus pamfi in Nigeria, and the Guinea multimammate mouse Mastomys erythroleucus in both Nigeria and Guinea. Virus strains from these animals were isolated in the BSL-4 laboratory and fully sequenced. Phylogenetic analyses of viral genes coding for glycoprotein, nucleoprotein, polymerase and matrix protein show that Lassa strains detected in M. erythroleucus belong to lineages III and IV. The strain from H. pamfi clusters close to lineage I (for S gene) and between II & III (for L gene). Discovery of new rodent hosts has implications for LASV evolution and its spread into new areas within West Africa.

BackgroundLassa fever, killing thousands of people annually, is the most reported viral zoonotic disease in Nigeria. Recently, different rodent species carrying diverse lineages of the Lassa virus (LASV) in addition to a novel Mobala-like genetic sequence were detected within the country. Here, screening 906 small mammal specimens from 11 localities for IgG antibodies and incorporating previous PCR detection data involving the same populations, we further describe arenavirus prevalence across Nigeria in relation to host species and geographical location.MethodsSmall mammals were trapped during the period 2011–2015 according to geographical location (endemic and non-endemic zones for Lassa fever), season (rainy and dry seasons between 2011 and 2012 for certain localities) and habitat (indoors, peridomestic settings and sylvatic vegetation). Identification of animal specimens from genera such as Mastomys and Mus (Nannomys) was assisted by DNA sequencing. Small mammals were tested for LASV IgG antibody using an indirect immunofluorescence assay (IFA).ResultsSmall mammals were infected in both the endemic and non-endemic zones for Lassa fever, with a wider range of species IgG-positive (n = 8) than those which had been previously detected to be PCR-positive (n = 3). IgG-positive species, according to number of infected individuals, were Mastomys natalensis (n = 40), Mastomys erythroleucus (n = 15), Praomys daltoni (n = 6), Mus baoulei (n = 5), Rattus rattus (n = 2), Crocidura spp. (n = 2), Mus minutoides (n = 1) and Praomys misonnei (n = 1). Multimammate mice (Mastomys natalensis and M. erythroleucus) were the most ubiquitously infected, with animals testing positive by either PCR or IgG in 7 out of the 11 localities sampled. IgG prevalence in M. natalensis ranged from 1% in Abagboro, 17–36 % in Eguare Egoro, Ekpoma and Ngel Nyaki, up to 52 % in Mayo Ranewo. Prevalence according to locality, season and age was not, however, statistically significant for M. natalensis in Eguare Egoro and Ekpoma, localities that were sampled longitudinally.ConclusionsOverall, our study demonstrates that arenavirus occurrence is probably more widely distributed geographically and in extent of host taxa than is currently realized. This expanded scope should be taken into consideration in Lassa fever control efforts. Further sampling should also be carried out to isolate and characterize potential arenaviruses present in small mammal populations we found to be seropositive.

Mastomys natalensis rodents are natural hosts for Lassa virus (LASV). Detection of LASV in 2 mitochondrial phylogroups of the rodent near the Niger and Benue Rivers in Nigeria underlines the potential for LASV emergence in fresh phylogroups of this rodent. A Mobala-like sequence was also detected in eastern Nigeria.

Context Following recent socioeconomic transformations in western and central Africa, the volume of bushmeat hunting, a traditional source of proteins and revenue for rural populations, has reached unsustainable levels. The morphological identification of species sold on bushmeat market stalls may be challenging because of the presence of cryptic taxa and smoked or processed carcasses. Aims To assess the contribution of DNA-typing to traditional bushmeat surveys. We conducted a case study at a roadside bushmeat market in Asejire, south-western Nigeria, to characterise the mammalian diversity and sketch out the dynamics of the bushmeat trade. Methods We generated a 402-bp Cytochrome b fragment using a ‘universal’ mitochondrial primer pair that successfully amplified across five mammalian orders, and used assignment procedures to assess the taxonomic identification of the traded species. We combined DNA-typing with morphological-based market surveys and questionnaires to half (n = 20) of the market stakeholders. Key results Our combined morphological–DNA-based survey revealed a total of 17 species, representing seven mammalian orders (Rodentia, Lagomorpha, Primates, Hyracoidea, Carnivora, Pholidota and Artiodactyla). DNA-typing allowed identifying the Walter’s duiker, a cryptic, newly described species from the Dahomey Gap, and diagnosing an unidentified primate as the white-throated monkey, Cercopithecus erythrogaster, a species of high conservation concern in Nigeria. K2P pairwise genetic distances among all species exceeded the 11% threshold, indicative of species-level distinction. The most hunted species were the Walter’s duiker and, to a lesser extent, the greater cane rat, Thryonomys swinderianus. Questionnaires to traders revealed that the Asejire roadside market was a straightforward trader–hunter system centralising off-takes from distant hunting sites. Conclusions We showed how mitochondrial DNA-typing combined with assignment procedures improved the characterisation of the mammalian diversity sold on bushmeat markets. The hunted mammalian community consisted of versatile, small- to medium-sized secondary forest species characteristic of the Dahomey Gap assemblage; their sustainable management is in doubt because of the lack of conservation and health awareness within the traders’ community. Implications Given the utility of mitochondrial DNA-typing in identifying species sold in bushmeat markets, we argue in favour of multi-entry investigations to reach a comprehensive characterisation of the bushmeat trade. The building of a web-accessible mtDNA database covering the spectrum of the species hunted for bushmeat would appear to be a valuable diagnostic tool that may help Nigeria and neighbouring countries to set up a rigorous monitoring of wildlife extirpation.

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