5.1 Genotyping of field samples reveals a correlation
between the 4.3kb SV and pyrethroid resistance.
Gounougou samples obtained from the deltamethrin 0.05% WHO tube
bioassays in 2018 (when the 4.3kb structural variant was not yet fixed)
were genotyped to determine any association between the 4.3kb SV and
deltamethrin resistance phenotype. The mortality rate for deltamethrin
was 49.8±11.6%. Genotyping of 77 mosquitoes exposed to deltamethrin (35
alive and 42 dead) revealed a strong association (χ2=33.8;
P<0.00001) between this structural variant and the
deltamethrin resistant phenotype, with 91.4% (32/35) of the survivors
24 hours post-exposure being homozygous for the structural variant
(SV+/SV+), 5.7% (2/35) of the survivors being heterozygous (SV+/SV-)
and only 2.9% (1/35) being homozygous without this SV (SV-/SV-) (Figure
3A; Table 1). Among the dead, the distribution of the genotypes was as
follows 26.2% (SV+/SV+), 16.7% (SV+/SV-) and 57.1% (SV-/SV-). The
odds ratio confirmed the positive association between the 4.3kb SV
genotype and the ability to survive exposure to deltamethrin, with
SV+/SV+ having a higher association with survival than the SV+/SV-
[OR: 10.2; CI: 1.8-56.5; P = 0.0080] and SV-/SV- [OR: 69.8; CI:
8.4-578.5; P = 0.0001]. The higher odds ratio obtained when comparing
the SV+/SV+ genotype to the SV+/SV- genotype (10.18) indicates an
additive effect of each 4.3 kb structural variant allele. Also, at the
allelic frequency, we observed that 94.3% of the alive had the SV+
allele against 5.7% lacking the 4.3kb SV allele showing that this
structural variant is strongly associated with the deltamethrin
resistance phenotype (OR: 29; CI: 11.6-73.2 ; P< 0.0001). Of
the dead, 65.5% lacked the 4.3kb SV (SV-), and 34.5% had the 4.3kb SV
(SV+), revealing a lower likelihood for the individuals with the 4.3kb
SV to be dead compared to those without (Figure 3B; Table 1).