Additional selection for insecticide resistance in urban malaria vectors: DDT resistance in Anopheles arabiensis from Bobo-Dioulasso, Burkina Faso

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In the city of Bobo-Dioulasso in Burkina Faso, Anopheles arabiensis has superseded Anopheles gambiae s.s. as the major malaria vector and the larvae are found in highly polluted habitats normally considered unsuitable for Anopheles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.

Figure 1. Microarray experimental design for investigating DDT resistance in An. arabiensis from a polluted breeding site in Dioulassoba.

Gene expression profiles of mosquitoes from Dioulassoba exposed (DSSBA RES) and unexposed (DSSBA CON) to DDT (4%) were compared to a laboratory An. arabiensis strain (MOZ SUS).

Figure 2. Venn diagram showing the pattern of differential expression among the microarray comparisons.

Microarray probes were considered significantly expressed at p<0.05 after the application of a multiple testing correction (Benjamini-Hochberg).

Figure 3. Fold-change in GSTD3 expression for microarray comparisons using quantitative qPCR.

Fold changes are expressed using the 2^−ΔΔCt formula with 95% C.I. .