Abstract
In the city of Bobo-Dioulasso in Burkina Faso, Anopheles arabiensis has superseded Anopheles gambiae s.s. as the major malaria vector and the larvae are found in highly polluted habitats normally considered unsuitable for Anopheles mosquitoes. Here we show that An. gambiae s.l. adults emerging from a highly polluted site in the city centre (Dioulassoba) have a high prevalence of DDT resistance (percentage mortality after exposure to diagnostic dose = 65.8% in the dry season and 70.4% in the rainy season, respectively). An investigation into the mechanisms responsible found an unexpectedly high frequency of the 1014S kdr mutation (allele frequency = 0.4), which is found at very low frequencies in An. arabiensis in the surrounding rural areas, and an increase in transcript levels of several detoxification genes, notably from the glutathione transferase and cytochrome P450 gene families. A number of ABC transporter genes were also expressed at elevated levels in the DDT resistant An. arabiensis. Unplanned urbanisation provides numerous breeding grounds for mosquitoes. The finding that Anopheles mosquitoes adapted to these urban breeding sites have a high prevalence of insecticide resistance has important implications for our understanding of the selective forces responsible for the rapid spread of insecticide resistant populations of malaria vectors in Africa.
Highlights
Almost half of the human population in Sub-Saharan Africa are projected to live in urban areas by 2030 [1]
We describe a DDT resistant population of An. arabiensis from a polluted breeding site in Bobo-Dioulasso and explore the genetic basis of this resistance
DDT Resistance in An. arabiensis from Dioulassoba To determine DDT resistance levels from the polluted site of Dioulassoba, a total of 313 and 262 female An. gambiae s.l. were exposed for one hour to DDT (4%) during the rainy (AugustSeptember, 2009) and dry season (January 2010), respectively
Summary
Almost half of the human population in Sub-Saharan Africa are projected to live in urban areas by 2030 [1]. Anopheles arabiensis is one of five mosquito species known to transmit malaria in African urban settings [3]. This member of the Anopheles gambiae species complex has a wide geographical range extending across the continent and is associated with drier climates and extensive land clearance [5]. Deforestation and urbanisation have created an arid environment into which An. arabiensis has invaded and adapted [6] and this species is the dominant malaria vector in several African cities [7,8,9,10]. The invasion of An. arabiensis into these ‘urban islands’ may be attributable to local adaptation to atypical breeding sites such as polluted water pools or ditches [8,11,12,13]
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