マラリアの制御と撲滅

Occurrence of Knockdown Resistance (kdr) Gene Mutation in Anopheles gambiae s.l. and Comparative Phenotypic Susceptibility to Synergized Natural Pyrethrum Formulation

Abstract

Kefa S Sum

Knockdown resistance (kdr) associated with single point mutation at the residue L1014 in the IIS6 transmembrane segment of the voltage gated sodium channel (vgsc)
gene in Anopheles gambiae s.l. is one of the known mechanisms of resistance against pyrethroid insecticides. This has emerged as a real threat to the continued effective use of insecticide-treated nets (ITNs) that rely mostly on pyrethroids as the active ingredient to control malaria vectors. There is, therefore, need for continuous monitoring the occurrence of vectors and development of alternative insecticide formulations as a strategy to manage kdr resistance and to sustain the use of this important technologies in malaria vector control. Anopheles gambiae s.l. mosquitoes were collected from Kisian, Ahero and Kipsitet, which are malaria endemic sites in western area of Kenya. The sibling species were identified using polymerase chain reaction (PCR) while genotyping for kdr mutation in the IIS4-IIS6 transmembrane segment of the vgsc was done using real time
PCR (RT-PCR). Susceptibility of the wild An. gambiae s.l and pink eyed An. gambiae s.s with fixed kdr resistance genes to synergized natural pyrethrum formulation
was assessed using WHO impregnated papers. Bioassay data data were subjected to analysis of variance (ANOVA) while those with coefficient of variation (CV) of >15% were transformation into logarithms before analysis. Treatment means were compared using least significant difference (LSD, P=0.05).
All the mosquitoes obtained from Kipsitet and Ahero areas were An. Arabiensis while in Kisian, 73% were An. arabiensis and 27% were An. gambiae s.s. No kdr genes
were detected in the An. arabiensis while there was 100% frequency of the L1014S kdr mutation in the An. gambiae s.s. Natural pyrethrum formulation achieved
significantly (P=0.0001) higher kill than pyrethroids against An. gambiae s.s. with kdr genes. High susceptibility of the An. gambiae s.s. with kdr mutation and wild
phenotypes to the synergized pyrethrum formulation provides crucial evidence for practical management of the spreading kdr and other resistance mechanisms to
pyrethroids in malaria vectors. The apparent lack of kdr resistance genes detected in An. arabiensis is proposed as a subject for further research.