Spatio-temporal patterns in kdr frequency in permethrin and DDT resistant Anopheles gambiae s.s. from Uganda

Abstract

The planned upscaling of vector control strategies requires insight into the epidemiological consequences of vector resistance. Therefore, the pyrethroid and DDT resistance status of Anopheles gambiae s.l. was assessed in Uganda from 2004 to 2006, and spatial and seasonal variations in knockdown resistance (kdr) frequencies were analyzed in terms of epidemiological significance. Anopheles gambiae s.l. was DDT and pyrethroid resistant in central and eastern Uganda. The L1014S kdr allele frequencies varied from 3% to 48% in An. gambiae s.s. Although the homozygous resistant genotype was the most prevalent genotype among survivors, the genotypes could not entirely explain the bioassay results. In the dry season, the kdr frequency was significantly higher in Plasmodium falciparum-infected mosquitoes, indicating that mosquitoes bearing a kdr mutation have a better adult survival, hence a higher likelihood of becoming infectious. This study showed that kdr might have an epidemiological impact that could jeopardize the vector control strategies.

Figure 1.

Mortality categories obtained for Anopheles gambiae s.l. in a WHO bioassay with DDT 4% and permethrin 0.75%.

Figure 2.

Impact of the season and the Plasmodium falciparum circumsporozoite status on the L1014S kdr allelic frequency in Tororo detected during the 1-year entomological study (2001–2002).

Figure 3.

Pooled kdr genotypes frequencies found in live (A) and dead (D) Anopheles gambiae s.s individuals (collected from 2004 to 2006). The P values found between surviving and dead Anopheles species are shown at the bottom.