Ndiaye, A. | bioRxiv Science

bioRxiv2020

Dynamics of residual malaria transmission in Central Western Senegal: Mapping the breeding sites of Anopheles gambiae s. l.

Despite the use of several effective control interventions in the central western Senegal, residual malaria transmission still occurring in some hotspots. In order to better understand the factors associated with this situation to better tailor targeted control actions, it is critical to unravel environmental and geographical factors underlying the persistence of the disease in study hotspot villages. Hotspots villages were defined as those reporting more than six indigenous malaria cases during the previous year. A total of ten villages, including seven hotspots and three non-hotspots, were surveyed. All potential mosquito breeding sites identified in and around the tenth study villages were regularly monitored between 2013 and 2017. This monitoring concerned the presence of anophelines larvae and the collection of epidemiological, hydrogeological, topographical and biogeographical data. Throughout the study area, the number of larval breeding sites inventoried and monitored over the study period ranged from 50 to 62. They were higher, with no significant difference, in hotspot sites than in non-hotspot sites for each year of monitoring with 62.3% (56/62) in 2013, 90.9% (50/55) in 2014, 90.3% (56/62) in 2015 and 86% (43/50) in 2017 (Fishers exact test; p = 1). The Hotspot villages were mostly characterized by saline or moderately saline hydro-morphic and halomorphic soils allowing water retention and a suitable presence of potential larval breeding sites. Whereas non-hotspot villages are characterized mainly by a high proportion of extremely permeable sandy-textured soils due to their porosity, which reduces water retention. The annual number of confirmed malaria cases was corelated relatively with the frequency and extent of breeding sites. Malaria cases were much more higher in the hamlets located near to the breeding sites of An. gambiae s.l then gradually decreases with their remoteness. This study has shown that the dynamics of larval breeding sites by their longevity, stability, proximity to houses and their positiveness rate for the presence of Anopheles larvae could be a determining factor in the persistence of malaria hotspots in central western Senegal. The results of this study shed more light on the environmental factors underlying the residual transmission and should make it possible to better organize vector control interventions for malaria elimination in west-central Senegal.

animal behavior and cognition↗

bioRxiv2019

Impact of historical and current features of the cityscape on the genetic structure of the house mouse (Mus musculus domesticus) in Dakar (Senegal, West Africa)

AO_SCPLOWBSTRACTC_SCPLOWPopulation genetic approaches may be used to investigate dispersal patterns of species living in highly urbanized environment in order to improve management strategies for biodiversity conservation or pest control. However, in such environment, population genetic structure may reflect both current features of the cityscape and urbanization history. This can be especially relevant when focusing on exotic commensal rodents that have been introduced in numerous primary colonial European settlements. Accounting for spatial and temporal cityscape heterogeneity to determine how past and recent demographic events may interplay to shape current population genetic structure of synanthropic rodents may provide useful insights to manage their populations. In this study, we addressed these issues by focusing on the house mouse, Mus musculus domesticus, in Dakar, Senegal, where the species may have been introduced as soon as Europeans settled in the middle of the nineteenth century. We examined genetic variation at one mitochondrial locus and 15 nuclear microsatellite markers from individuals sampled in 14 sampling sites representing different stages of urbanization history and different socio-economic environments in Dakar. We used various approaches, including model-based genetic clustering and model-free smoothing of pairwise genetic estimates. We further linked observed spatial genetic patterns to historical and current features of Dakar cityscape using random forest and Bayesian conditional autoregressive models. Results are consistent with an introduction of the house mouse at colonial time and the current genetic structure exhibits a gradient-like pattern reflecting the historical process of spatially continuous expansion of the city from the first European settlement. The genetic patterns further suggest that population dynamics of the house mouse is also driven by the spatial heterogeneity of the current cityscape, including socio-economics features, that translate in habitat quality. Our results highlight the potential importance of accounting for past demographic events to understand spatial genetic patterns of nonnative invasive commensal rodents in highly urbanized environment.

ecology↗