Climate change is impacting the spread/intensity of vector-borne diseases, including malaria, and accelerating evolutionary/adaptive changes in vector species. These changes including chromoso-mal inversions and overexpression and/or changes in allele frequencies of thermotoler-ance-associated genes, may facilitate insecticide resistance through pleiotropy. This study investi-gated the impact of thermotolerance on pyrethroid resistance in four populations of malaria vector An. gambiae, from savanna/sub-Sahel of northern Nigeria. Anopheles coluzzii and An. gambiae were the only malaria vectors found, sympatric in all the sites, with the former species predominant. High thermotolerance was observed, with no mortality at 38°C, and LT50 of ~44°C. Significantly high permethrin resistance was observed (mortality <50%) in heat-hardened (44°C) larvae from two sites, BUK and Pantami, compared with control, and heat-hardened adult females from Auyo (mortality = 3.00%±1.20, χ2 = 5.83, p<0.01) compared with control (12.00%±4.65). The 2La chromosomal inver-sion was detected at ~50% in larvae and 58% in adult females. Significant association was observed (OR = 7.2, p<0.03) between permethrin resistance and 2La/+a rearrangement compared with 2L+a/+a, in BUK larvae. For all sites permethrin resistance correlated with 2La/a homozygosity in adult fe-males [OR = 5.02, p=0.01). qRT-PCR identified 6 genes commonly induced/overexpressed, including heat shock protein 70 (AGAP004581) which was 2468x and 5x overexpressed in heat-hardened and permethrin-resistant females, respectively, trehalose-6-phosphate synthase (AGAP008227), and ionotropic glutamate receptor genes, IR25a (AGAP010272) and IR21a (AGAP008511). This study highlights challenges associated with insecticide-based malaria vector control, and the epidemiological significance of taking climate variables into account for design/choice of control measures.

Increased levels of insecticide resistance in major malaria vectors such as Anopheles funestus threaten the effectiveness of insecticide-based control programmes. Understanding the landscape features impacting the spread of resistance makers is necessary to design suitable resistance management strategies. Here we examined the influence of the highest mountain in West Africa (Mount Cameroon; 4,100 meters elevation) on the spread of metabolic and target-site resistance alleles in An. funestus populations. Vector composition varied across the four localities surveyed along the altitudinal cline with major vectors exhibiting high parity rate (80.5%). Plasmodium infection rates ranged from 0.79% (An. melas) to 4.67% (An. funestus). High frequencies of GSTe2R (67% - 81%) and RdlR (49% - 90%) resistance alleles were observed in An. funestus throughout the study area, with GSTe2R frequency increasing with altitude whereas the opposite is observed for RdlR. Patterns of genetic diversity and population structure analyses revealed high levels of polymorphisms with 12 and 16 haplotypes respectively for GSTe2 and Rdl. However, the reduced diversity patterns of resistance allele carriers revealed signatures of positive selection on the two genes across the study area irrespective of the altitude. Despite slight variations associated with the altitude, the spread of resistance alleles suggest that control strategies could be implemented against malaria vectors across mountainous landscapes.

Assessing the genetic diversity of metabolic resistance genes such as cytochrome P450s helps to understand the dynamics and evolution of resistance in the field. Here, we analysed the polymor-phisms of CYP6M2 and CYP6P4 associated with pyrethroid resistance in Anopheles coluzzii and An. gambiae, to detect potential resistance markers. Field-caught resistant mosquitoes and susceptible lab-strains were crossed and F4 was exposed to permethrin for 15min and 90min to discriminate highly susceptible (HS) and highly resistant (HR) mosquitoes respectively. Significant permethrin mortality reduction was observed after pre-exposure to PBO, suggesting P450s genes involvement. QPCR analysis revealed significant over-expression of CYP6M2 (FC=19.57 [95%CI 13.96-25.18] for An. coluzzii; 10.16 [7.86-12.46] for An. gambiae) and CYP6P4 (FC=6.73 [6.15-7.30] An. coluzzii; 23.62 [26.48-20.76] An. gambiae). Full-gene and ≈1kb upstream were sequenced. For CYP6M2, upstream region shows low diversity in HR and HS (overall Hd=0.49, π=0.018), whereas the full-gene shows allelic-variation but without evidence of ongoing selection. CYP6P4 upstream region showed a lower diversity in HR (Hd=0.48) than HS (Hd=0.86) of An. gambiae. These results highlighted that CYP6P4-associated resistance is potentially driven by modification in upstream region. However further work is needed to determine the real causative variants which will help design rapid detec-tion tools.

(1) Background: Malaria remains a global public health problem. Unfortunately, the resistance of malaria vectors to insecticides commonly used threatens disease control and elimination efforts. Molecular mechanisms helping some malaria vectors to now survive to greater doses of insecticides remains poorly understood. Here, we elucidated the pattern of resistance escalation in the main malaria vector Anopheles gambiae in a pesticide-driven agricultural hotspot in Cameroon and its impact on vector control tools; (2) Methods: Larval stages and indoor blood-fed females (F0) were collected in Mangoum in May and November and forced to lay eggs; the emerging mosquitoes were used for WHO tube, synergist and cone tests. Molecular identification was done using SINE PCR whereas TaqMan-based PCR was used for genotyping of L1014F/S and N1575Y kdr and the G119S-ACE1 resistance markers. Transcription profile of candidate resistance genes was performed using qRT-PCR methods. Characterization of the breeding water and soil from Mangoum was also performed using HPLC technique; (3) Results: An. gambiae s.s. was the only species in Mangoum with 4.10 % infection with Plasmodium. These mosquitoes were resistant to all the four classes of insecticides with mortality rates &lt;7% for pyrethroids and DDT and &lt;54% for carbamates and organophophates. This population also exhibited high resistance intensity to pyrethroids (permethrin, alpha-cypermethrin and deltamethrin) after exposure to 5X and 10X discriminating doses and Synergist assays with PBO revealed only a partial recovery of susceptibility to permethrin, alpha-cypermethrin and deltamethrin. Only PBO-based nets (Olyset plus and permaNet 3.0) and Royal Guard showed an optimal efficacy. A high amount of alpha-cypermethrin was detected in breeding sites (5.16 fold LOD) suggesting ongoing selection from agricultural pesticides. The 1014F-kdr allele was fixed (100%) whereas the 1575Y-kdr (37.5%) and the 119S Ace-1R (51.1%) are moderately present. Elevated expression of P450s respectively in permethrin and deltamethrin resistant mosquitoes [CYP6M2 (10 and 34-fold), CYP6Z1(17 and 29-fold), CYP6Z2 (13 and 65-fold), CYP9K1 (13 and 87-fold)] supports their role in the observed resistance besides other mechanisms including chemosensory genes as SAP1 (28 and 13-fold), SAP2 (5 and 5-fold),SAP3 (24 and 8-fold) and cuticular genes as CYP4G16 (6 and 8-fold) and CYP4G17 (5 and 27-fold). However, these candidate genes were not associated with resistance escalation as expression level did not differ significantly between 1x, 5x and 10x surviving mosquitoes. (4) Conclusions: Intensive and multiple resistance is being selected in malaria vectors from pesticide-based agricultural hotspot of Cameroon leading to loss of efficacy of pyrethroid-only nets. Further studies are needed to decipher the molecular basis underlying such resistance escalation to better assess its impact on control interventions.

Growing resistance is reported to carbamate insecticides in malaria vectors in Cameroon. However, the contribution of acetylcholinesterase (Ace-1) to this resistance remains uncharacterised. Here, we established that the G119S mutation is driving resistance to carbamates in Anopheles gambiae populations from Cameroon. Insecticide bioassay on field collected mosquitoes from Bankeng, a locality in southern Cameroon, showed high resistance to the carbamates bendiocarb (64.8 ± 3.5 % mortality) and propoxur (55.71 ± 2.9 %) but a full susceptibility to the organophosphate fenithrothion. The TaqMan genotyping of the G119S mutation in field-collected adults revealed the presence of this resistance allele (39%). A significant correlation was observed between the Ace-1^R and carbamate resistance at allelic [(bendiocarb; OR = 75.9; P<0.0001) and (propoxur; OR= 1514; P<0.0001)] and genotypic [RR vs SS (bendiocarb; OR = 120.8; P<0.0001) and (propoxur; OR= 3277; P<0.0001) levels. Furthermore, the presence of the mutation was confirmed by sequencing an Ace-1 portion flanking codon 119. The cloning of this fragment revealed a likely duplication of Ace-1 in Cameroon as mosquitoes exhibited at least three distinct haplotypes. Phylogenetic analyses showed that the predominant Ace-1^R allele is identical to that from West Africa suggesting a recent introduction of this allele in Central Africa from the West. The spread of this Ace-1^R represents a serious challenge to future implementation of IRS-based interventions using carbamates or organophosphates in Cameroon

Background: New insecticides with novel modes of action such as neonicotinoids have recently been recommended for public health use by WHO. Resistance monitoring of such novel insecticides requires a robust protocol to monitor the development of resistance in natural populations. In this study, we comparatively used three different solvents to assess the susceptibility of malaria vectors to neonicotinoids across Africa.Methods: Mosquitoes were collected from May to July 2021 from three agricultural settings in Cameroon (Njombe-Penja, Nkolondom, and Mangoum), the Democratic Republic of Congo (Ndjili-Brasserie), Ghana (Atatam), and Uganda (Mayuge). Using the CDC bottle test, we compared the effect of three different solvents (ethanol, acetone, acetone+MERO) on the efficacy of neonicotinoids against Anopheles gambiae s.l. In addition, TaqMan assays were used to genotype key pyrethroid-resistant markers in An. gambiae and to evaluate potential cross-resistance between pyrethroids and clothianidin.Results: Lower mortalities were observed for all populations when using absolute ethanol or acetone alone as solvent (11.4- 51.9% mortality for Nkolondom, 31.7- 48.2% for Mangoum, 34.6- 56.1% for Mayuge, 39.4- 45.6% for Atatam, 83.7- 89.3% for Congo and 71.05- 95.9% for Njombe pendja) compared to acetone + MERO for which 100% mortality was observed for all the populations. Synergist assays (PBO, DEM and DEF) revealed a significant increase of mortality suggesting that metabolic resistance mechanisms are contributing to the reduced susceptibility. A negative association was observed between the L1014F-kdr mutation and clothianidin resistance with a greater frequency of homozygote resistant mosquitoes among the dead than among survivors (OR=0.5; P=0.02). However, the I114T-GSTe2 was in contrast significantly associated with a greater ability to survive clothianidin with a higher frequency of homozygote resistant among survivors than other genotypes (OR=2.10; P=0.013). Conclusions: This study revealed a contrasted susceptibility pattern depending on the solvents with ethanol/acetone resulting in lower mortality, thus possibly overestimating resistance, whereas the addition of MERO consistently increased the efficacy of neonicotinoids in terms of percentage mortalities and time to final mortality. The addition of MERO could however prevent the early detection of resistance development. We therefore recommend monitoring susceptibility using both acetone alone and acetone+MERO (8-10µg/ml for clothianidin) to capture the accurate resistance profile of the mosquito populations.