Molecular characterization of pyrethroid knockdown resistance (kdr) in the major malaria vector Anopheles gambiae s.s.

Abstract

Pyrethroid-impregnated bednets are playing an increasing role for combating malaria, especially in stable malaria areas. More than 90% of the current annual malaria incidence (c. 500 million clinical cases with up to 2 million deaths) is in Africa where the major vector is Anopheles gambiae s.s. As pyrethroid resistance has been reported in this mosquito, reliable and simple techniques are urgently needed to characterize and monitor this resistance in the field. In insects, an important mechanism of pyrethroid resistance is due to a modification of the voltage-gated sodium channel protein recently shown to be associated with mutations of the para-type sodium channel gene. We demonstrate here that one of these mutations is present in certain strains of pyrethroid resistant A. gambiae s.s. and describe a PCR-based diagnostic test allowing its detection in the genome of single mosquitoes. Using this test, we found this mutation in six out of seven field samples from West Africa, its frequency being closely correlated with survival to pyrethroid exposure. This diagnostic test should bring major improvement for field monitoring of pyrethroid resistance, within the framework of malaria control programmes.

Synergistic interaction between two cockroach sodium channel mutations and a tobacco budworm sodium channel mutation in reducing channel sensitivity to a pyrethroid insecticide

“…1) in segment 6 of domain II (IIS6) is associated with kdr and kdr-type resistance (Miyazaki et al, 1996;Williamson et al, 1996;Dong, 1997). Subsequently, the same mutation was found in other important insect pests, including diamondback moth, Plutella xylostella (Martinez-Torres et al, 1997), horn fly, Haematobia irritans (Guerrero et al, 1997), mosquitoes, Anopheles gambiae and Culex pipiens (Martinez-Torres et al, 1998), aphids, Myzus persicae (Martinez-Torres et al, 1999), and Colorado potato beetle, Leptinotarsa decemlineata (Lee et al, 1999a). Conversely, in pyrethroid-resistant tobacco budworm (Heliothis virescens), an L1029H mutation in IIS6 is associated with pyrethroid resistance .…”

Monooxygenase Levels and Knockdown Resistance (kdr) Allele Frequencies in Anopheles gambiae and Anopheles arabiensis in Kenya

“…Several studies in western Africa An. gambiae populations found extremely high kdr allele frequency based on larval samples (e.g., 20-96% in Ivory Coast [Martinez-Torres et al 1998], and 89-96% in Burkina Faso [Diabate et al 2002]). We recommend using adult samples or using larvae from many diverse aquatic habitats for insecticide resistance surveillance to minimize sampling bias.…”

“…Metabolic detoxification is generally associated with increased monooxygenase activity, causing not only pyrethroid resistance but also cross-resistance to unrelated compounds (Berge et al 1998, Liu et al 2006. The target site of pyrethroids is the voltage-gated sodium channel.…”

“…The target site of pyrethroids is the voltage-gated sodium channel. A point mutation in the region II of the para-type sodium channel gene causes a change in affinity between the insecticide and its binding site on the sodium channel, and induces a phenotype termed knockdown resistance (kdr) in a range of insects (Williamson et al 1996, Dong 1997, Jamroz et al 1998, Martinez-Torres et al 1998, 1999, Ranson et al 2000. Insensitivity at the sodium channel target sites also leads to crossresistance between different classes of insecticides (Brengues et al 2003).…”

“…Permethrin knock-down resistance has arisen independently at least twice in Africa. In west Africa, kdr was caused by a leucine-phenylalanine substitution at position 1014 of the sodium channel gene (L1014F) whereas a different mutation (leucine-serine substitution) at the same amino acid position (L1014S) was associated with kdr resistance in Kenya in both A. gambiae and A. arabiensis (Martinez-Torres et al 1998;Ranson et al 2000;Stump et al 2004). However, the L1014F mutation has been detected in An.…”