Abstract
BackgroundIndoor residual spraying (IRS) has again become popular for malaria control in Africa. This combined with the affirmation by WHO that DDT is appropriate for use in the absence of longer lasting insecticide formulations in some malaria endemic settings, has resulted in an increase in IRS with DDT as a major malaria vector control intervention in Africa. DDT was re-introduced into Mozambique's IRS programme in 2005 and is increasingly becoming the main insecticide used for malaria vector control in Mozambique. The selection of DDT as the insecticide of choice in Mozambique is evidence-based, taking account of the susceptibility of Anopheles funestus to all available insecticide choices, as well as operational costs of spraying.Previously lambda cyhalothrin had replaced DDT in Mozambique in 1993. However, resistance appeared quickly to this insecticide and, in 2000, the pyrethroid was phased out and the carbamate bendiocarb introduced. Low level resistance was detected by biochemical assay to bendiocarb in 1999 in both An. funestus and Anopheles arabiensis, although this was not evident in WHO bioassays of the same population.MethodsSentinel sites were established and monitored for insecticide resistance using WHO bioassays. These assays were conducted on 1–3 day old F1 offspring of field collected adult caught An. funestus females to determine levels of insecticide resistance in the malaria vector population. WHO biochemical assays were carried out to determine the frequency of insecticide resistance genes within the same population.ResultsIn surveys conducted between 2002 and 2006, low levels of bendiocarb resistance were detected in An. funestus, populations using WHO bioassays. This is probably due to significantly elevated levels of Acetylcholinesterase levels found in the same populations. Pyrethroid resistance was also detected in populations and linked to elevated levels of p450 monooxygenase activity. One site had shown reduction in pyrethroid resistance since the base line in 1999.
Highlights
Indoor residual spraying (IRS) has again become popular for malaria control in Africa
Malaria vector control relies on the use of effective insecticides, most commonly through indoor residual spraying (IRS) or insecticide-treated nets (ITN)
DDT was rapidly introduced into public health and malaria control campaigns, and was the main insecticide used in the WHO malaria eradication campaign carried out between 1955 to 1969 [5]
Summary
Indoor residual spraying (IRS) has again become popular for malaria control in Africa. This combined with the affirmation by WHO that DDT is appropriate for use in the absence of longer lasting insecticide formulations in some malaria endemic settings, has resulted in an increase in IRS with DDT as a major malaria vector control intervention in Africa. Malaria vector control relies on the use of effective insecticides, most commonly through indoor residual spraying (IRS) or insecticide-treated nets (ITN). The increased number of reports of insecticide resistant Anopheles species in Africa [3] is a threat to the success of insecticide-based malaria control programmes. Insecticide resistance in the vector is one of the major reasons given for the failure of the WHO campaign [5], but there is little evidence to support this claim in Africa [3,6]
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