Yvan Gaetan Fotso-Toguem

Arboviruses transmitted by Aedes aegypti and Aedes albopictus , including Zika, yellow fever and especially dengue and chikungunya, represent a growing public health concern in Africa. Insecticide‐based strategies remain essential for the prevention and control of arboviral outbreaks. However, insecticide resistance in Ae. aegypti is globally widespread and appears to be rising in sub‐Saharan Africa. Here, we reviewed the distribution and phenotypic and molecular evidence of insecticide resistance in Ae. aegypti across sub‐Saharan Africa and summarized the underlying resistance mechanisms and key knowledge gaps. Bibliographic databases were searched for studies published between January 2010 and December 2023. The review identified 40 studies from 18 of 47 countries in sub‐Saharan Africa. Among adults mosquitoes, resistance to dichlorodiphenyltrichloroethane (DDT) and pyrethroids was reported in multiple studies across West and Central Africa, while resistance to carbamates was also documented in several countries, comparatively fewer studies reported resistance to organophosphates. For larvae 7 of 40 studies assessed susceptibility to temephos, with potential resistance reported in only one study. Molecular investigations identified five kdr mutations including F1534C, V1016I, V410L, V1016G and S989P in 12 countries while metabolic resistance involving cytochrome P450s, carboxylesterases, glutathione S‐transferases and other detoxification enzymes was reported in a smaller number of studies and countries. Overall, the evidence base remains geographically uneven and limited for several insecticide classes and resistance mechanisms. This review highlights important knowledge gaps, including the limited assessment of larvicides, emerging adulticide options, resistance intensity and Aedes‐targeted vector control interventions, and underscores the need for more systematic and standardized insecticide resistance surveillance across sub‐Saharan Africa.

The effectiveness of malaria vector control is increasingly threatened by widespread insecticide resistance, particularly to pyrethroids. In response, the World Health Organization recommends dual-active ingredients (dual-A.I.) insecticide-treated nets (ITNs) in resistant settings. This study evaluated the efficacy of several dual-A.I. ITNs in two experimental hut trial sites an area with high insecticide resistant malaria vectors in Tanzania with differing vector species composition and bionomics. Five ITNs were evaluated: a pyrethroid-only net (MAGNet®), three pyrethroid-piperonyl butoxide (PBO) nets (OlysetTM Plus, Veeralin®, and PermaNet® 3.0), one dual-A.I. net (Interceptor® G2; chlorfenapyr + alpha-cypermethrin), and an untreated control net. Mosquitoes were collected from huts, morphologically identified, and monitored for mortality up to 72 h. WHO cone and tunnel tests using susceptible An. gambiae s.s. were conducted for quality control, while field-collected mosquitoes were used for bio-efficacy monitoring. Molecular species identification was performed using PCR assays, and genomic DNA was extracted from An. funestus s.l. and An. gambiae s.l. collected from the trials. All ITNs met WHO bio-efficacy criteria in cone and tunnel tests. An. gambiae s.l. predominated in Mwagagala (77%) but was rare in Magu (4%), where An. funestus complex was dominant. In Magu, Interceptor® G2 and Veeralin® achieved significantly higher mortality than MAGNet® at 24 h (53% and 45% vs 24%) and 72 h (61% and 53% vs 24%). In contrast, no significant mortality differences were observed among ITNs in Mwagagala. High resistance intensity was detected in both vector groups (mortality An. funestus from Magu, the 4.3 kb-SV resistant genotype was fixed, while G454A-CYP9K1 resistance was highly prevalent (RR: 0.70– 1.00). Interceptor® G2 and Veeralin® outperformed the pyrethroid-only reference net against An. funestus complex but not against predominantly An. arabiensis populations.

Background: The double burden of malaria and helminthiasis in children poses an obvious public health challenge, particularly in terms of anemia morbidity. While both diseases frequently geographically overlap, most studies focus on mono-infection and general prevalence surveys without molecular analysis. The current study investigated the epidemiological determinants of malaria, schistosomiasis, and geohelminthiasis transmission among children in the North Region of Cameroon. Methodology: School and pre-school children aged 3–15 year-of-age were enrolled from three communities in March 2021 using a community cross-sectional design. Capillary-blood samples were obtained, and each was examined for malaria parasites using rapid-diagnostic-test (RDT), microscopy, and PCR while hemoglobin level was measured using a hemoglobinometer. Stool samples were analyzed for Schistosoma mansoni, S. guineensis, and soil-transmitted-helminthiasis (STH) infections using the Kato Katz method, and urine samples were assessed for the presence of S. haematobium eggs (including hybrids) using the standard urine filtration technique. Result: A malaria prevalence of 56% (277/495) was recorded by PCR as opposed to 31.5% (156/495) by microscopy and 37.8% (186/495) by RDT. Similarly, schistosomiasis was observed at prevalence levels of up to 13.3% (66/495) overall [S. haematobium (8.7%); S. mansoni (3.8%); mixed Sh/Sm (0.6%); mixed Sh/Sm/Sg (0.2%). Both infections were higher in males and the 3–9 year-of-age groups. A high frequency of PCR reported P. falciparum mono-infection of 81.9% (227/277) and mixed P. falciparum/P. malariae infection of 17.3% (48/277) was observed. Malaria-helminths co-infections were observed at 13.1% (65/495) with marked variation between P. falciparum/S. haematobium (50.8%, 33/65); P. falciparum/S. mansoni (16.9%, 11/65) and P. falciparum/Ascaris (9.2%, 6/65) (χ² = 17.5, p = 0.00003). Anemia prevalence was 32.9% (163/495), categorically associated with P. falciparum (45.8%, 104/227), Pf/Sh (11.5%, 26/227), and Pf/Sm (3.9%, 9/227) polyparasitism. Conclusion: Polyparasitism with malaria and helminth infections is common in school-aged children despite periodic long-lasting insecticide-treated nets (LLINs) distribution and regular school-based praziquantel (for schistosomiasis) and albendazole (for STH) campaigns. Co-existence of Plasmodium parasites and helminths infections notably Schistosoma species among children may concurrently lead to an increase in Plasmodium infection with an enhanced risk of anemia, highlighting the necessity of an integrated approach for disease control interventions.

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 analyzed the polymorphisms of CYP6M2 and CYP6P4, associated with pyrethroid resistance in Anopheles coluzzii and Anopheles gambiae, to detect potential resistance markers. Field-caught resistant mosquitos and susceptible lab strains were crossed, and F4 was exposed to permethrin for 15 min and 90 min to discriminate highly susceptible (HS) and highly resistant (HR) mosquitos, respectively. Significant permethrin mortality reduction was observed after pre-exposure to PBO, suggesting the gene involvement of P450s. qPCR analysis revealed significant overexpression 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 ≈1 kb upstream were sequenced. For CYP6M2, the 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 that will help design rapid detection tools.

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.

Constant assessment of insecticide resistance levels is mandatory to implement adequate malaria control tools, but little information is available on the annual dynamics of resistance. We, therefore, monitored variations in resistance in Anopheles gambiae s.l. over four seasons during 2 years in two localities of Yaoundé: urban Etoa‐Meki and peri‐urban Nkolondom. Mosquitoes were collected seasonally at larval stage and reared to adults for insecticide susceptibility tests and molecular analysis of resistance mechanisms. Anopheles coluzzii was found in Etoa‐Meki and An. gambiae in Nkolondom. Low mortalities to pyrethroids were observed (permethrin kdr allele shows a high frequency (0.9), associated with overexpression of metabolic genes (Cyp6M2, Cyp6P4, Cyp9K1, Cyp6Z1, and Cyp6Z2) varying significantly seasonally. This study reveals an escalation in resistance to pyrethroids in Yaoundé's malaria vectors with seasonal variations. An adequate choice of the implementation period of punctual vector control actions according to the resistance profile will help to potentiate the desired effect and thus improve its efficiency.

Background: Cameroon is considering the implementation of indoor residual spraying (IRS) as a complementary measure to control malaria in the context of high pyrethroid resistance in major malaria vectors. Non-pyrethroid insecticide classes such as organophosphates and carbamates may be utilized in IRS due to widespread pyrethroid resistance. However, the success of this strategy depends on good knowledge of the resistance status of malaria vectors to carbamates and organophosphates. Here, we assessed the susceptibility profile of Anopheles gambiae sensu lato with respect to carbamates and organophosphate and the distribution of the molecular mechanism underlying resistance to these insecticides. Methods: Anopheles gambiae s.l. mosquitoes were collected from nine settings across the country and bio-assayed with bendiocarb, propoxur and pirimiphos-methyl. The Ace-1 target-site G119S mutation was genotyped using a TaqMan assay. To investigate the polymorphism in the Ace-1 gene, a region of 924 base pairs in a sequence of the gene was amplified from both live and dead females of An. gambiae exposed to bendiocarb. Results: Pirimiphos-methyl induced full mortality in An. gambiae s.l. from all study sites, whereas for carbamates, resistance was observed in four localities, with the lowest mortality rate recorded in Mangoum (17.78 ± 5.02% for bendiocarb and 18.61 ± 3.86% for propoxur) in the southern part of Cameroon. Anopheles coluzzii was found to be the predominant species in the northern tropical part of the country where it is sympatric with Anopheles arabiensis. In the localities situated in southern equatorial regions, this species was predominant in urban settings, while An. gambiae was the most abundant species in rural areas. The G119S Ace-1 target-site mutation was detected only in An. gambiae and only in the sites located in southern Cameroon. Phylogenetic analyses showed a clustering according to the phenotype. Conclusion: The occurrence of the Ace-1 target-site substitution G119S in An. gambiae s.l. populations highlights the challenge associated with the impending deployment of IRS in Cameroon using carbamates or organophosphates. It is therefore important to think about a resistance management plan including the use of other insecticide classes such as neonicotinoids or pyrrole to guarantee the implementation of IRS in Cameroon. Graphical

The African mirid bug (Sahlbergella singularis) is the most economically important insect pest in cocoa farms. Pesticide management, although controversial due to the adverse effects of these substances on the environment and on human health, remains the main option used for controlling this pest. In the recent decades, the development of alternative approaches to synthetic pesticides is a requirement. Therefore, we used neem oil (NO) and ethanolic extracts (EE) from leaves at different concentrations to evaluate, in vitro, their insecticidal potentials against mirids. Mirid mortality increased significantly with increase in concentrations, values ranged from 32.5 to 92.5 % for EE and 52.5 to 97.5 % for NO. Apart from negative controls, Tween 80 and distilled water, that showed significant low mortality rates, both extracts revealed effectiveness comparable to the reference insecticide used in controlling mirids, except for EE by ingestion. Mirids treated by contact showed significantly high mortality rates (72.5 to 97.5 %) compared to those treated by ingestion (32.5 to 70.0 %). The greatest biological effectiveness values were obtained at a concentration of 8 % by contact exposure: 0.88 ml/ml (NO) and 0.73 g/ml (EE) for LC50 and ≈1 day to both extracts for LT₅₀. Given effectiveness comparable to that of the insecticide, both tested extracts should be considered as effective biopesticides for IPM against mirids, especially S. singularis.