Insecticide resistance of malaria mosquitoes from Guinea Conakry
Date
2009-04-23T05:35:16Z
Authors
Vezenegho, Samuel Bumuh
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Abstract
Introduction: There is only limited information on malaria vector species
composition, vector status and susceptibility status in Guinea Conakry. This work
provides more information from three localities (Boffa, Siguiri and Mount Nimba)
with very different ecological settings.
Methods: Anopheles mosquitoes were collected resting inside houses. Field
bioassays were performed on An. gambiae s.l using the standard WHO protocol.
Further species identification by PCR, laboratory bioassay by WHO standards,
biochemical enzyme analysis, sporozoite ELISA, kdr detection by PCR and
pyrosequencing were performed.
Results: Of 600 specimens, 494 (82.3%) were An. gambiae and 2 (0.33%) An.
arabiensis. Plasmodium infection rates varied from 1.25 to 5%. Resistance to 4%
dieldrin and 0.1% bendiocarb need confirmation in Boffa and to 0.05% deltamethrin
and 5% malathion in Siguiri. Resistance to DDT, dieldrin and bendiocarb occurred in
Siguiri and Mount Nimba. F1 progeny of wild An. gambiae s.s exposed to pirimiphos methyl indicated elevated esterase and monooxygenase enzymes involved in
metabolic detoxification of insecticides. The Kdr-w mutation is present in both the M
and S forms of An. gambiae. Kdr genotypes by pyrosequencing and sequencing were
in agreement but the standard PCR method gave 28% false positives.
Conclusion: Both molecular forms of An. gambiae are implicated in malaria
transmission, occur in sympatry and exhibit some degree of resistance to insecticides
at all localities. The mechanism of resistance is unclear. Pyrosequencing is more
accurate for detecting kdr than the standard PCR method. Vector control interventions need to be tailored to each site based on the data collected by on-going
monitoring and surveillance.