Insecticide resistance in malaria vector mosquitoes in a gold mining town in Ghana and implications for malaria control.

Malaria control programmes in Africa, for the most part, address only treatment of the disease and supply of insecticide treated bed nets. The impact of these restricted programmes has been limited and new approaches are being advocated, including integrated vector management strategies and partnerships with industry. Mosquito surveys were carried out for AngloGold/Ashanti in preparation for their implementation of an integrated malaria control programme at the Obuasi gold mine in Ghana. Malaria vectors that were collected inside houses were identified to species and molecular forms by PCR, and tested for insecticide resistance using standard WHO bioassays and molecular target site insensitivity (kdr) assays. Species were identified as An. funestus s.s. and An. gambiae S and M forms. The An. gambiae S form samples showed resistance to DDT, pyrethroids and carbamates while An. funestus was resistant to DDT and carbamates. The An. gambiae M form occurred in very low numbers and could not be assessed reliably for resistance. The standard PCR assay for detection of the kdr mutation in An. gambiae S form showed little association with pyrethroid resistance. Subsequent sequencing of the II56 domain containing the kdr mutation from nine surviving mosquitoes showed that eight were homozygous resistant and one heterozygous. This correlated with the bioassay results and with previous studies on West African An. gambiae, but raised concerns about the reliability of the PCR assay for detection of the kdr mutation. As a result of these investigations AngloGold/Ashanti are implementing, in addition to treatment and case management, a vector control programme that includes insecticide resistance management by alternation of various classes of insecticides for house spraying, supply of ITNs, screening of houses and environmental management where appropriate, i.e. integrated vector management.