Invasive rodents have been responsible for the diffusion worldwide of many zoonotic agents, thus representing major threats for public health. Cities are important hubs for people and goods exchange and are thus expected to play a pivotal role in invasive commensal rodent dissemination. Yet, data about urban rodents' ecology, especially invasive vs. native species interactions, are dramatically scarce. Here, we provide results of an extensive survey of urban rodents conducted in Niamey, Niger, depicting the early stages of rodent bioinvasions within a city. We explore the species-specific spatial distributions throughout the city using contrasted approaches, namely field sampling, co-occurrence analysis, occupancy modelling and indicator geostatistics. We show that (i) two species (i.e. rural-like vs. truly commensal) assemblages can be identified, and that (ii) within commensal rodents, invasive (Rattus rattus and Mus musculus) and native (Mastomys natalensis) species are spatially segregated. Moreover, several pieces of arguments tend to suggest that these exclusive distributions reflect an ongoing native-to-invasive species turn over. The underlying processes as well as the possible consequences for humans are discussed.

Leptospirosis essentially affects human following contact with rodent urine-contaminated water. As such, it was mainly found associated with rice culture, recreational activities and flooding. This is also the reason why it has mainly been investigated in temperate as well as warm and humid regions, while arid zones have been only very occasionally monitored for this disease. In particular, data for West African countries are extremely scarce. Here, we took advantage of an extensive survey of urban rodents in Niamey, Niger, in order to look for rodent-borne pathogenic Leptospira species presence and distribution across the city. To do so, we used high throughput bacterial 16S-based metabarcoding, lipL32 gene-targeting RT-PCR, rrs gene sequencing and VNTR typing as well as GIS-based multivariate spatial analysis. Our results show that leptospires seem absent from the core city where usual Leptospira reservoir rodent species (namely R. rattus and M. natalensis) are yet abundant. On the contrary, L. kirschneri was detected in Arvicanthis niloticus and Cricetomys gambianus, two rodent species that are restricted to irrigated cultures within the city. Moreover, the VNTR profiles showed that rodent-borne leptospires in Niamey belong to previously undescribed serovars. Altogether, our study points towards the importance of market gardening in maintain and circulation of leptospirosis within Sahelian cities. In Africa, irrigated urban agriculture constitutes a pivotal source of food supply, especially in the context of the ongoing extensive urbanization of the continent. With this in mind, we speculate that leptospirosis may represent a zoonotic disease of concern also in arid regions that would deserve to be more rigorously surveyed, especially in urban agricultural settings. We surveyed rodent-borne Leptospira in rodents from Niamey, the capital town of Niger, using bacterial metabarcoding, RT-PCR, sequencing, VNTR typing and GIS-based geostatistics. Two new serovars of Leptospira kirschneri were identified in Arvicanthis niloticus and Cricetomys gambianus, two species that inhabit exclusively urban irrigated gardens. Since no rodent-borne leptospires could be found in the core city, our results point towards the importance of urban agriculture in the maintaining and the circulation of these bacteria in cities from semi-arid regions where they are usually poorly documented and even hardly looked for. Accordingly, this is one of the very rare mentions of these zoonotic agents in Sahel, and the first one in Niger. Keeping in mind the critical role of urban gardening for food security in extensively growing West African cities, we believe that leptospirosis should be more closely scrutinized in Sahelian countries where numerous cases of human fevers are of unknown origin.

Based on compiled small mammal trapping data collected over 12 years from Benin and Niger (3701 individual records from 66 sampling sites), located in mainland Africa, we here describe the small mammal community assemblage in urban habitats along the commercial axis connecting the two countries, from the seaport of Cotonou to the Sahelian hinterland, with a particular focus on invasive species. In doing so, we document extant species distributions, which highlight the risks of continuing the range expansion of three synanthropic invasive rodent species, namely black rats (Rattus rattus), brown rats (R. norvegicus), and house mice (Mus musculus). Using various diversity estimates and community ecology approaches, we detect a latitudinal gradient of species richness that significantly decreased Northward. We show that shrews (Crocidura) represent a very important component of micro-mammal fauna in West African towns and villages, especially at lower latitudes. We also demonstrate that invasive and native synanthropic rodents do not distribute randomly in West Africa, which suggests that invasive species dynamics and history differ markedly, and that they involve gradual, as well as human-mediated, long distance dispersal. Patterns of segregation are also observed between native Mastomys natalensis and invasive rats R. rattus and R. norvegicus, suggesting potential native-to-invasive species turn over. Consequences of such processes, especially in terms of public health, are discussed.

Cercarial emission of schistosomes is a determinant in the transmission to the definitive host and constitutes a good marker to identify which definitive host is responsible for transmission, mainly in introgressive hybridization situations. Our goal was to test the hypothesis that micro-mammals play a role inSchistosoma haematobium,S.bovis, and/orS.haematobiumxS.bovistransmission. Small mammal sampling was conducted in seven semi-lacustrine villages of southern Benin. Among the 62 animals trapped, 50 individuals were investigated forSchistosomaadults and eggs: 37Rattus rattus, 3Rattus norvegicus, 9Mastomys natalensis, and 1Crocidura olivieri.Schistosomaadults were found in fourR. rattusand twoM. natalensis, with a local prevalence reaching 80% and 50%, respectively.Two cercarial chronotypes were found fromBulinus globosusexperimentally infected with miracidia extracted from naturally infectedM. natalensis: a late diurnal and nocturnal chronotype, and an early diurnal, late diurnal, and nocturnal chronotype. The cytochrome C oxidase subunit I mtDNA gene of the collected schistosomes (adults, miracidia, and cercariae) belonged to theS.bovisclade. Eleven internal transcribed spacer rDNA profiles were found; four belonged toS.bovisand seven toS.haematobiumxS.bovis. These molecular results together with the observed multi-peak chronotypes addM. natalensisas a new host implicated inS.haematobiumxS.bovistransmission. We discuss the origin of the new chronotypes which have become more complex with the appearance of several peaks in a 24-h day. We also discuss how the new populations of offspring may optimize intra-host ecological niche, host spectrum, and transmission time period.