Dynamics of multiple insecticide resistance in the malaria vector Anopheles gambiae in a rice growing area in south-western Burkina Faso
Insecticide resistance of the main malaria vector, Anopheles gambiae, has been reported in south-western Burkina Faso, West Africa. Cross-resistance to DDT and pyrethroids was conferred by alterations at site of action in the sodium channel, the Leu-Phe kdr mutation; resistance to organophosphates and carbamates resulted from a single point mutation in the oxyanion hole of the acetylcholinesterase enzyme designed as ace-1R.
Methods: An entomological survey was carried out during the rainy season of 2005 at Vallee du Kou, a rice growing area in south-western Burkina Faso. At the Vallee du Kou, both insecticide resistance mechanisms have been previously described in the M and S molecular forms of An.
gambiae. This survey aimed i) to update the temporal dynamics and the circumsporozoite infection rate of the two molecular forms M and S of An.
gambiae; ii) to update the frequency of the Leu-Phe kdr mutation within these forms; and, finally iii) to investigate the occurrence of the ace-1R mutation.Mosquitoes collected by indoor residual collection and by human landing catches were counted and morphologically identified. Species and molecular forms of An.
gambiae, ace-1R and Leu-Phe kdr mutations were determined using PCR techniques. The presence of the circumsporozoite protein of Plasmodium falciparum was determined using ELISA.
Results: Anopheles gambiae populations were dominated by the M form.
However the S form occurred in relative important proportion towards the end of the rainy season with a maximum peak in October at 51%. Sporozoite rates were similar in both forms.
The frequency of the Leu-Phe kdr mutation in the S form reached a fixation level while it is still spreading in the M form. Furthermore, the ace-1R mutation prevailed predominately in the S form and has just started spreading in the M form.
The two mutations occurred concomitantly both in M and S populations.
Conclusion: These results showed that the Vallee du Kou, a rice growing area formerly occupied mainly by M susceptible populations, is progressively colonized by S resistant populations living in sympatry with the former.
As a result, the distribution pattern of insecticide resistance mutations shows the occurrence of both resistance mechanisms concomitantly in the same populations. The impact of multiple resistance mechanisms in M and S populations of An.
gambiae on vector control measures against malaria transmission, such as insecticide-treated nets (ITNs) and indoor residual spraying (IRS), in this area is discussed.
Author: Kounbobr Roch Dabire, Abdoulaye Diabate, Luc Djogbenou, Ali Ouari, Raphael N'Guessan, Jean-Bosco Ouedraogo, Jean-Marc Hougard, Fabrice Chandre and Thierry Baldet
Credits/Source: Malaria Journal 2008, 7:188
Published on: 2008-09-25
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