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Background  At the end of 2005, a nationwide long-lasting insecticide-treated net (LLIN) distribution targeting the most vulnerable populations was implemented throughout Niger. A large number of studies in Africa have reported the existence of anopheline populations resistant to various insecticides, partly due to knockdown resistance ( kdr ) mutations, but few operational wide-scale control programmes were coupled with the monitoring of such mutations. The distribution of the  kdr-west  ( kdr-w)  Leu-Phe mutation was studied in  Anopheles gambiae  s.l. populations from Niger and temporal variations were monitored following the nationwide LLIN implementation.    Methods  Mosquitoes were collected from 14 localities during the wet seasons of 2005, 2006 and 2007 with additional sampling in the capital city, Niamey. After morphological identification of  Anopheles gambiae  s.l. specimens, DNA extracts were used for the determination of species and molecular forms of the  Anopheles gambiae  complex and for the detection of the  kdr-w  mutation.    Results  Around 1,500 specimens collected in the three consecutive years were analysed. All  Anopheles arabiensis  specimens analysed were homozygous susceptible, whereas the few  Anopheles gambiae  S forms exhibited a high overall  kdr-w  frequency. The M form samples exhibited a low overall  kdr-w  frequency before the LLIN distribution, that increased significantly in the two wet season collections following the LLIN distribution. Higher  kdr  frequencies were repeatedly noticed within host-seeking females compared to resting ones in indoor collections. In addition, preliminary results in M form urban populations from Niamey showed far higher  kdr  frequencies than in all of the rural sites studied.    Discussion  This study describes the first case of  kdr  mutation in  Anopheles gambiae  populations from Niger. It is suspected that the LLIN have caused the important temporal increase of  kdr-w  mutation observed during this study. While the  kdr  mutation is still found at a low level, this rapid increase could potentially lead to high  kdr  frequencies within a few years.    Conclusion  These results are of prime importance in the effort to document multiple effects of operational control programmes on mosquito vectors, and to conceive sustainable control strategies for future malaria control programmes.

malaria journal

Evidence of increasing Leu-Phe knockdown resistance mutation in Anopheles gambiae from Niger following a nationwide long-lasting insecticide-treated nets implementation