Abstract
BackgroundThe distribution of insecticide treated nets (ITN) has been dramatically scaled up in eastern and central Sudan. Resistance to insecticides has already been reported in this region and there is an urgent need to develop appropriate resistance management strategies, which requires detailed information on the extent and causes of resistance. This study assessed resistance to permethrin and DDT in seven populations of Anopheles arabiensis from Sudan.ResultsThree out of the seven populations were defined as resistant to permethrin and five of six populations resistant to DDT according to WHO criteria. The 1014F kdr allele was present in all six populations tested and the presence of this allele was significantly correlated with resistance to permethrin (P = 0.0460). While homozygous 1014F individuals were statistically not more likely to survive (53.7%) permethrin than to be killed (38.6%) by the diagnostic dose, there was no difference in the likelihood of permethrin survival in heterozygotes (P = 0.7973). The susceptible genotypes were more likely to be killed by permethrin exposure than to survive (P = 0.0460). The 1014F allele failed to confer a survival advantage to the WHO diagnostic dose of DDT in either the homozygous or heterozygous state. The 1014S allele was not detected in any of the populations tested.ConclusionThe kdr allele is certainly contributing to the extensive resistance to permethrin and DDT in Sudan but the high number of DDT (43%) and permethrin (16.7%) survivors that did not contain either kdr alleles suggests that other resistance mechanisms are also present in these populations. The high frequency of permethrin resistance throughout central and eastern Sudan is a cause of great concern for malaria control activities.
Highlights
The distribution of insecticide treated nets (ITN) has been dramatically scaled up in eastern and central Sudan
ITNs and, to a large extent, indoor residual spraying (IRS) are highly dependent on pyrethroid insecticides
Because the distance between the sites surveyed within the states is shorter, each state was treated as one population except Sennar and Gadaref where Mayirno, Al Faw and Al Shuwak were considered different populations due to the relatively long distances which separate them (Figure 1)
Summary
The distribution of insecticide treated nets (ITN) has been dramatically scaled up in eastern and central Sudan. Ongoing strategies of malaria vector control rely greatly on the use of indoor residual spraying (IRS) and insecticide-treated nets (ITNs). The number of countries that employed IRS as vector control strategy. ITNs and, to a large extent, IRS are highly dependent on pyrethroid insecticides. The widespread use of this class of insecticide increases the risk of resistance. The situation may be accelerated by the reintroduction of DDT in several countries in Africa as cross-resistance between these insecticide classes can occur as a result of amino acid substitutions in the shared target site. All major malaria vectors in Africa have developed resistance to these insecticides and the resistance alleles appear to be spreading at an exceptionally rapid rate [3]
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