Increasing globalization has promoted the spread of exotic species, including disease vectors. Understanding the evolutionary processes involved in such colonizations is both of intrinsic biological interest and important to predict and mitigate future disease risks. The Aedes aegypti mosquito is a major vector of dengue, chikungunya and Zika, the worldwide spread of which has been facilitated by Ae. aegypti's adaption to human-modified environments. Understanding the evolutionary processes involved in this invasion requires characterization of the genetic make-up of the source population (s). The application of approximate Bayesian computation (ABC) to sequence data from four nuclear and one mitochondrial marker revealed that African populations of Ae. aegypti best fit a demographic model of lineage diversification, historical admixture and recent population structuring. As ancestral Ae. aegypti were dependent on forests, this population history is consistent with the effects of forest fragmentation and expansion driven by Pleistocene climatic change. Alternatively, or additionally, historical human movement across the continent may have facilitated their recent spread and mixing. ABC analysis and haplotype networks support earlier inferences of a single out-of-Africa colonization event, while a cline of decreasing genetic diversity indicates that Ae. aegypti moved first from Africa to the Americas and then to Asia. ABC analysis was unable to verify this colonization route, possibly because the genetic signal of admixture obscures the true colonization pathway. By increasing genetic diversity and forming novel allelic combinations, divergence and historical admixture within Africa could have provided the adaptive potential needed for the successful worldwide spread of Ae. aegypti.

Aedes aegypti mosquitoes originated in Africa and are thought to have spread recently to Southeast Asia, where they are the major vector of dengue. Thirteen microsatellite loci were used to determine the genetic population structure of A. aegypti at a hierarchy of spatial scales encompassing 36 sites in Myanmar, Cambodia and Thailand, and two sites in Sri Lanka and Nigeria. Low, but significant, genetic structuring was found at all spatial scales (from 5 to >2000 km) and significant FIS values indicated genetic structuring even within 500 m. Spatially dependent genetic-clustering methods revealed that although spatial distance plays a role in shaping larger-scale population structure, it is not the only factor. Genetic heterogeneity in major port cities and genetic similarity of distant locations connected by major roads, suggest that human transportation routes have resulted in passive long-distance migration of A. aegypti. The restricted dispersal on a small spatial scale will make localized control efforts and sterile insect technology effective for dengue control. Conversely, preventing the establishment of insecticide resistance genes or spreading refractory genes in a genetic modification strategy would be challenging. These effects on vector control will depend on the relative strength of the opposing effects of passive dispersal.

The current distribution of Bantu languages is commonly considered to be a consequence of a relatively recent population expansion (3-5kya) in Central Western Africa. While there is a substantial consensus regarding the centre of origin of Bantu languages (the Benue River Valley, between South East Nigeria and Western Cameroon), the identification of the area from where the population expansion actually started, the relation between the processes leading to the spread of languages and peoples and the relevance of local migratory events remain controversial. In order to shed new light on these aspects, we studied Y chromosome variation in a broad dataset of populations encompassing Nigeria, Cameroon, Gabon and Congo. Our results evidence an evolutionary scenario which is more complex than had been previously thought, pointing to a marked differentiation of Cameroonian populations from the rest of the dataset. In fact, in contrast with the current view of Bantu speakers as a homogeneous group of populations, we observed an unexpectedly high level of interpopulation genetic heterogeneity and highlighted previously undetected diversity for lineages associated with the diffusion of Bantu languages (E1b1a (M2) sub-branches). We also detected substantial differences in local demographic histories, which concord with the hypotheses regarding an early diffusion of Bantu languages into the forest area and a subsequent demographic expansion and migration towards eastern and western Africa.

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BackgroundStudies implemented to evaluate the success of Long-lasting insecticidal nets (LLIN) distribution campaigns are often limited to ownership and utilization rates, neglecting other factors that directly affect the efficacy of the tool in malaria control. This study investigates sleeping habits and net maintenance behaviour in addition to LLIN ownership, utilization and the challenges associated with LLIN use among residents in Ilorin City where the tool has been massively distributed.MethodsA cross-sectional survey was conducted using pre-tested interviewer-administered questionnaire to obtain information from randomly selected household respondents in Ilorin, the Kwara State Capital. The study was conducted in July 2012, about sixteen months after the March 2011 distribution of LLIN in the locality. The results were analyzed using the EPI INFO 2007 version.ResultsLLIN ownership (85%) and utilization (37%) rates improved compared to earlier reports, though 29% of net users have noticed holes in the nets even as 26% claimed to have actually experienced mosquito bites under it. Most (92%) of the respondents who slept under LLIN the previous night before the study spent the first five hours of the night (19.00-23.00 hr) outdoors while 88% also engage in inappropriate net washing practices. All the LLIN users claimed to have experienced at least one malaria episode while 43% have had two or more episodes within the past twelve months.ConclusionThe use of LLIN among the respondents in this study was accompanied by chancy sleeping habits, inappropriate net maintenance practices and repeated experience of mosquito bites under the nets. This shows the need to sustain the will and confidence of LLIN users in this area through frequent monitoring and surveillance visits targeted at enlightening the people on habits that increase malaria exposure risks as well as proper use and maintenance of LLIN for maximum malaria vector control benefits.