Dynamics of multiple insecticide resistance in the malaria vector Anopheles gambiae in a rice growing area in South-Western Burkina Faso.
BACKGROUND
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 Vallée du Kou, a rice growing area in south-western Burkina Faso. At the Vallée 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.


CONCLUSIONS
These results showed that the Vallée 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.
Dabiré
Kounbobr Roch
KR
Institut de Recherche en Science de la Santé, Centre Muraz, Bobo-Dioulasso, Burkina Faso. dabire_roch@hotmail.com
Diabaté
Abdoulaye
A
Djogbenou
Luc
L
Ouari
Ali
A
N'Guessan
Raphaël
R
Ouédraogo
Jean-Bosco
JB
Hougard
Jean-Marc
JM
Chandre
Fabrice
F
Baldet
Thierry
T
D000110:Acetylcholinesterase / Q000235:genetics; D000483:Alleles; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000235:genetics; D002050:Burkina Faso; D004797:Enzyme-Linked Immunosorbent Assay; D005787:Gene Frequency; D006801:Humans; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D020125:Mutation, Missense; D016133:Polymerase Chain Reaction / Q000379:methods; D015800:Protozoan Proteins / Q000097:blood; D015222:Sodium Channels / Q000235:genetics
D007306:Insecticides; D015800:Protozoan Proteins; D015222:Sodium Channels; C041595:circumsporozoite protein, Protozoan; D000110:Acetylcholinesterase