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      Dengue and yellow fever virus vectors: seasonal abundance, diversity and resting preferences in three Kenyan cities

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          Abstract

          Background

          The transmission patterns of dengue (DENV) and yellow fever (YFV) viruses, especially in urban settings, are influenced by Aedes ( Stegomyia) mosquito abundance and behavior. Despite recurrent dengue outbreaks on the Kenyan coast, these parameters remain poorly defined in this and other areas of contrasting dengue endemicity in Kenya. In assessing the transmission risk of DENV/YFV in three Kenyan cities, we determined adult abundance and resting habits of potential Aedes ( Stegomyia) vectors in Kilifi (dengue-outbreak prone), and Nairobi and Kisumu (no dengue outbreaks reported). In addition, mosquito diversity, an important consideration for changing mosquito-borne disease dynamics, was compared.

          Methods

          Between October 2014 and June 2016, host-seeking adult mosquitoes were sampled using CO 2-baited BG-Sentinel traps (12 traps daily) placed in vegetation around homesteads, across study sites in the three major cities. Also, indoor and outdoor resting mosquitoes were sampled using Prokopack aspirators. Three samplings, each of five consecutive days, were conducted during the long-rains, short-rains and dry season for each city. Inter-city and seasonal variation in mosquito abundance and diversity was evaluated using general linear models while mosquito-resting preference (indoors vs outdoors) was compared using Chi-square test.

          Results

          Aedes aegypti, which comprised 60% ( n = 7772) of the total 12,937 host-seeking mosquitoes collected, had comparable numbers in Kisumu (45.2%, n = 3513) and Kilifi (37.7%, n = 2932), both being significantly higher than Nairobi (17.1%, n = 1327). Aedes aegypti abundance was significantly lower in the short-rains and dry season relative to the long-rains ( P < 0.0001). Aedes bromeliae, which occurred in low numbers, did not differ significantly between seasons or cities. Mosquito diversity was highest during the long-rains and in Nairobi. Only 10% ( n = 43) of the 450 houses aspirated were found positive for resting Ae. aegypti, with overall low captures in all areas. Aedes aegypti densities were comparable indoors/outdoors in Kilifi; but with higher densities outdoors than indoors in Kisumu and Nairobi.

          Conclusions

          The presence and abundance of Ae. aegypti near human habitations and dwellings, especially in Kilifi/Kisumu, is suggestive of increased DENV transmission risk due to higher prospects of human vector contact. Despite low abundance of Ae. bromeliae suggestive of low YFV transmission risk, its proximity to human habitation as well as the observed diversity of potential YFV vectors should be of public health concern and monitored closely for targeted control. The largely outdoor resting behavior for Ae. aegypti provides insights for targeted adult vector control especially during emergency outbreak situations.

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          Most cited references34

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          A new, cost-effective, battery-powered aspirator for adult mosquito collections.

          We report the development of a new mosquito aspirator with the same aspiration capacity (airflow) of the CDC Backpack Aspirator (CDC-BP), but smaller and lighter (0.8 kg without battery), less expensive (US$45-70), easier to build, and compatible with the use of telescoping extension poles to access hard-to-reach locations. The performance of this new aspirator, named "Prokopack," was compared with the CDC-BP in laboratory settings as well as in paired collections in combined sewer overflow (CSO) tunnels in Atlanta, GA, and indoor mosquito collections in Iquitos, Peru. The difference in suction power between both aspirators (average, 0.29-0.43 m/s) was negligible. However, 2.3 times more mosquitoes were collected using the Prokopack in the upper wall (>1.5 m) and ceilings of CSO tunnels than with the CDC-BP in lower walls. Indoor collection in Iquitos yielded significantly more total mosquito numbers [including Culex pipiens complex, Culex (melanoconion) sp., and Mansonia sp.] and Aedes aegypti (L.) in the Prokopack than in the CDC-BP. Our results demonstrate the effectiveness of the Prokopack to collect different mosquito species in different epidemiological settings.
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            Vectors of Chikungunya virus in Senegal: current data and transmission cycles.

            Chikungunya fever is a viral disease transmitted to human beings by Aedes genus mosquitoes. From 1972 to 1986 in Kédougou, Senegal, 178 Chikungunya virus strains were isolated from gallery forest mosquitoes, with most of them isolated from Ae. furcifer-taylori (129 strains), Ae. luteocephalus (27 strains), and Ae. dalzieli (12 strains). The characteristics of the sylvatic transmission cycle are a circulation periodicity with silent intervals that last approximately three years. Few epidemics of this disease have been reported in Senegal. The most recent one occurred in 1996 in Kaffrine where two Chikungunya virus strains were isolated from Ae. aegypti. The retrospective analysis of viral isolates from mosquitoes, wild vertebrates, and humans allowed to us to characterize Chikungunya virus transmission cycles in Senegal and to compare them with those of yellow fever virus.
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              Worldwide patterns of genetic differentiation imply multiple 'domestications' of Aedes aegypti, a major vector of human diseases.

              Understanding the processes by which species colonize and adapt to human habitats is particularly important in the case of disease-vectoring arthropods. The mosquito species Aedes aegypti, a major vector of dengue and yellow fever viruses, probably originated as a wild, zoophilic species in sub-Saharan Africa, where some populations still breed in tree holes in forested habitats. Many populations of the species, however, have evolved to thrive in human habitats and to bite humans. This includes some populations within Africa as well as almost all those outside Africa. It is not clear whether all domestic populations are genetically related and represent a single 'domestication' event, or whether association with human habitats has developed multiple times independently within the species. To test the hypotheses above, we screened 24 worldwide population samples of Ae. aegypti at 12 polymorphic microsatellite loci. We identified two distinct genetic clusters: one included all domestic populations outside of Africa and the other included both domestic and forest populations within Africa. This suggests that human association in Africa occurred independently from that in domestic populations across the rest of the world. Additionally, measures of genetic diversity support Ae. aegypti in Africa as the ancestral form of the species. Individuals from domestic populations outside Africa can reliably be assigned back to their population of origin, which will help determine the origins of new introductions of Ae. aegypti.
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                Author and article information

                Contributors
                sagha@icipe.org , aghasheila@yahoo.com
                dtchouassi@icipe.org
                ADBastos@zoology.up.ac.za
                rsang@icipe.org
                Journal
                Parasit Vectors
                Parasit Vectors
                Parasites & Vectors
                BioMed Central (London )
                1756-3305
                29 December 2017
                29 December 2017
                2017
                : 10
                : 628
                Affiliations
                [1 ]ISNI 0000 0004 1794 5158, GRID grid.419326.b, International Centre of Insect Physiology and Ecology, ; P. O Box 30772-00100, Nairobi, Kenya
                [2 ]ISNI 0000 0001 2107 2298, GRID grid.49697.35, Department of Zoology and Entomology, , University of Pretoria, ; Private Bag 20, Hatfield, 0083 South Africa
                [3 ]ISNI 0000 0001 0155 5938, GRID grid.33058.3d, Arbovirus/Viral Hemorrhagic Fever Laboratory, Centre for Virus Research, Kenya Medical Research Institute, ; P. O Box 54840-00200, Nairobi, Kenya
                Author information
                http://orcid.org/0000-0002-5480-6865
                Article
                2598
                10.1186/s13071-017-2598-2
                5747025
                29284522
                4d55a33b-fbfa-4bd2-ab76-7fa8ab99844c
                © The Author(s). 2017

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 29 August 2017
                : 17 December 2017
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/100000002, National Institutes of Health;
                Award ID: 1R01AI099736-01A1
                Award Recipient :
                Funded by: FundRef http://dx.doi.org/10.13039/501100001655, Deutscher Akademischer Austauschdienst;
                Categories
                Research
                Custom metadata
                © The Author(s) 2017

                Parasitology
                aedes aegypti,aedes bromeliae,vector abundance,mosquito diversity,resting preference,urbanization,kenya,dengue and yellow fever risk

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