Abstract:
BACKGROUND : The Democratic Republic of the Congo (DRC) is characterized as a holoendemic malaria area with the
main vectors being Anopheles funestus and members of the Anopheles gambiae complex. Due to political instability
and socio-economic challenges in the region, knowledge of insecticide resistance status and resistance mechanisms
in these vectors is limited. Mosquitoes were collected from a mining site in the north-eastern part of the country and,
following identification, were subjected to extensive testing for the target-site and biochemical basis of resistance.
Quantitative real-time PCR was used to assess a suite of 10 genes frequently involved in pyrethroid and dichlorodiphenyltrichloroethane
(DDT) resistance in An. gambiae females and males. In An. funestus, gene expression microarray
analysis was carried out on female mosquitoes.
RESULTS : In both species, deltamethrin resistance was recorded along with high resistance and suspected resistance
to DDT in An. gambiae and An. funestus, respectively. A total of 85% of An. gambiae carried the kdr mutations as either
homozygous resistant (RR) (L1014S, L1014F or both) or heterozygous (RS), however only 3% carried the rdl mutant
allele (RS) and no ace-1 mutations were recorded. Synergist assays indicated a strong role for P450s in deltamethrin
resistance in both species. In An. gambiae, analysis of transcription levels showed that the glutathione-S-transferase,
GSTS1-2, produced the highest fold change in expression (7.6-fold in females and 31-fold in males) followed by GSTE2,
thioredoxin peroxidase (TPX2), and cytochrome oxidases (CYP6M2 and CYP6P1). All other genes tested produced
fold change values below 2. Microarray analysis revealed significant over-transcription of cuticular proteins as well as
CYP6M7, CYP6P9a and CYP6P9b in insecticide resistant An. funestus.
CONCLUSIONS : These data show that high levels of deltamethrin resistance in the main malaria vector species, conferred
by enzymatic detoxification, are present in the DRC.
