Extensive permethrin and DDT resistance in Anopheles arabiensis from eastern and central Sudan

Background

The 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.

Results

Three 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.

Conclusion

The 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.