Abstract
BackgroundAlthough adult mosquito vectors of sylvatic arbovirus [yellow fever (YFV), dengue-2 (DENV-2) and chikungunya (CHIKV)] have been studied for the past 40 years in southeastern Senegal, data are still lacking on the ecology of larval mosquitoes in this area. In this study, we investigated the larval habitats of mosquitoes and characterized their seasonal and spatial dynamics in arbovirus foci.MethodsWe searched for wet microhabitats, classified in 9 categories, in five land cover classes (agriculture, forest, savannah, barren and village) from June, 2010 to January, 2011. Mosquito immatures were sampled monthly in up to 30 microhabitats of each category per land cover and bred until adult stage for determination.ResultsNo wet microhabitats were found in the agricultural sites; in the remaining land covers immature stages of 35 mosquito species in 7 genera were sampled from 9 microhabitats (tree holes, fresh fruit husks, decaying fruit husks, puddles, bamboo holes, discarded containers, tires, rock holes and storage containers). The most abundant species was Aedes aegypti formosus, representing 30.2% of the collections, followed by 12 species, representing each more than 1% of the total, among them the arbovirus vectors Ae. vittatus (7.9%), Ae. luteocephalus (5.7%), Ae. taylori (5.0%), and Ae. furcifer (1.3%). Aedes aegypti, Cx. nebulosus, Cx. perfuscus, Cx. tritaeniorhynchus, Er. chrysogster and Ae. vittatus were the only common species collected from all land covers. Aedes furcifer and Ae. taylori were collected in fresh fruit husks and tree holes. Species richness and dominance varied significantly in land covers and microhabitats. Positive associations were found mainly between Ae. furcifer, Ae. taylori and Ae. luteocephalus. A high proportion of potential enzootic vectors that are not anthropophilic were found in the larval mosquito fauna.ConclusionsIn southeastern Senegal, Ae. furcifer and Ae. taylori larvae showed a more limited distribution among both land cover and microhabitat types than the other common species. Uniquely among vector species, Ae. aegypti formosus larvae occurred at the highest frequency in villages. Finally, a high proportion of the potential non-anthropophilic vectors were represented in the larval mosquito fauna, suggesting the existence of unidentified sylvatic arbovirus cycles in southeastern Senegal.
Highlights
Adult mosquito vectors of sylvatic arbovirus [yellow fever (YFV), dengue-2 (DENV-2) and chikungunya (CHIKV)] have been studied for the past 40 years in southeastern Senegal, data are still lacking on the ecology of larval mosquitoes in this area
chikungunya virus (CHIKV) has been isolated from 11 mosquito species and 3 different monkeys species during amplifications of the sylvatic cycle in the region, the data indicate that the main vectors (Ae. furcifer, Ae. taylori, Ae. luteocephalus) as well as vertebrate hosts are the same as those for DENV-2
Regardless of the land cover type, immature mosquitoes were most often detected in decaying fruit husks, of which 100% contained at least one larva or pupa, followed by fresh fruit husks (89%), tree holes (75%) and tires (73%)
Summary
Adult mosquito vectors of sylvatic arbovirus [yellow fever (YFV), dengue-2 (DENV-2) and chikungunya (CHIKV)] have been studied for the past 40 years in southeastern Senegal, data are still lacking on the ecology of larval mosquitoes in this area. 5 amplifications of the sylvatic cycle were detected between 1980 and 2000 in Kédougou During these amplifications, large numbers of DENV-2 strains were isolated from mosquitoes, mainly from Ae. furcifer, Ae. luteocephalus, Ae. taylori, Ae. aegypti formosus, and Ae. vitattus, one strain from the serum of a wild patas monkey (Erythrocebus patas), and four strains from human sera [5,6,7,8]. CHIKV has been isolated from 11 mosquito species and 3 different monkeys species during amplifications of the sylvatic cycle in the region, the data indicate that the main vectors (Ae. furcifer, Ae. taylori, Ae. luteocephalus) as well as vertebrate hosts (monkeys and humans) are the same as those for DENV-2. Transmission of CHIKV may differ in subtle ways from that of sylvatic DENV-2, due to the possible existence of additional CHIKV vectors and vertebrate hosts other than monkeys, such as galagos (Galago senegalensis), palm squirrels (Xerus erythropus), and bats (Scotophillus sp) [1]
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