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International audience; The cosmopolitan black rat, Rattus rattus, has invaded many cities throughout the world. Although the species is responsible for major damages to food stocks and crops and is involved in the maintenance, circulation and transmission of many zoonotic pathogens to humans and animals, a lot remains to be known about its eco-evolutionary characteristics, especially in highly modified environments like the urban habitat. In particular, very few studies were conducted on the genetic structure of urban black rat populations, which is yet a prerequisite for defining effective management units. Here, we focus on the population genetics of Rattus rattus in Cotonou, Benin. Forty different localities were sampled throughout the city and 457 individuals were genotyped using 18 microsatellite markers. Our results reveal two poorly distinguishable but significant genetic clusters, one of each side of Cotonou channel, that tend to homogenize into a single group due to probable gene flow between the two shores. Implications in terms of management units and rodent control are discussed.

Bioinvasion is a major public health issue because it can lead to the introduction of pathogens in new areas and favours the emergence of zoonotic diseases. Rodents are prominent invasive species, and act as reservoirs in many zoonotic infectious diseases. The aim of this study was to determine the link between the distribution and spread of two parasite taxa (Leishmania spp. and Trypanosoma lewisi) and the progressive invasion of Senegal by two commensal rodent species (the house mouse Mus musculus domesticus and the black rat Rattus rattus). M. m. domesticus and R. rattus have invaded the northern part and the central/southern part of the country, respectively. Native and invasive rodents were caught in villages and cities along the invasion gradients of both invaders, from coastal localities towards the interior of the land. Molecular diagnosis of the two trypanosomatid infections was performed using spleen specimens. In the north, neither M. m. domesticus nor the native species were carriers of these parasites. Conversely, in the south, 17.5% of R. rattus were infected by L. major and 27.8% by T. lewisi, while very few commensal native rodents were carriers. Prevalence pattern along invasion gradients, together with the knowledge on the geographical distribution of the parasites, suggested that the presence of the two parasites in R. rattus in Senegal is of different origins. Indeed, the invader R. rattus could have been locally infected by the native parasite L. major. Conversely, it could have introduced the exotic parasite T. lewisi in Senegal, the latter appearing to be poorly transmitted to native rodents. Altogether, these data show that R. rattus is a carrier of both parasites and could be responsible for the emergence of new foci of cutaneous leishmaniasis, or for the transmission of atypical human trypanosomiasis in Senegal., Author summary Biological invasions (the introduction and adaptation of living organisms to a new environment) are increasingly frequent due to worldwide intensification of human-associated exchanges. They can lead to the introduction of pathogens in new areas and favour the emergence of diseases. Rodents are prominent invasive species, and act as reservoirs in many infectious diseases. The aim of our study was to determine the link between the distribution and spread of two parasites, Leishmania spp. and Trypanosoma lewisi, and the progressive invasion of Senegal by two commensal rodent species, the house mouse Mus musculus domesticus, and the black rat Rattus rattus. We identified R. rattus as a potential reservoir for Leishmania major and T. lewisi in the southern part of Senegal. The presence of these two pathogens in R. rattus may be of different origins. The invader R. rattus could have been locally contaminated with L. major. Conversely, T. lewisi infection could have been introduced in Senegal by R. rattus, and seems to be poorly transmitted to native rodents. Altogether, these data show that R. rattus is a carrier of both parasites, and could be responsible for the emergence of new foci of cutaneous leishmaniasis or for the transmission of atypical human trypanosomiasis in Senegal.