Spatial Heterogeneity of CYP9K1 Gene Overexpression Driving Cross-Resistance to Insecticide in Anopheles Mosquitoes Across Sub-Saharan Africa: A Systematic Review and Meta-Analysis

Insecticide resistance in Anopheles mosquitoes poses a growing challenge to malaria elimination efforts across sub-Saharan Africa, threatening the continued effectiveness of frontline interventions. Among the metabolic mechanisms driving resistance, the cytochrome P450 monooxygenase gene CYP9K1 has been increasingly associated with detoxification and cross-resistance to multiple insecticide classes, particularly pyrethroids. This review assessed spatial heterogeneity in CYP9K1 overexpression (log₂ fold change) in cross-resistant Anopheles mosquito populations across sub-Saharan Africa. This systematic review was conducted in accordance with PRISMA guidelines, drawing data from PubMed, Scopus, Web of Science, ScienceDirect, BioMed Central, and Google Scholar (2015-2025). Random-effects models using restricted maximum likelihood (REML) estimation were applied in JASP, alongside subgroup, sensitivity, and publication bias analyses. Out of 17,163 retrieved records, 11 studies met the inclusion criteria, representing data from six sub-Saharan African countries. The pooled log₂ fold change for CYP9K1 expression was 1.910 (95% CI: 1.274-2.545; p < 0.001), confirming significant upregulation in resistant mosquito populations. Subgroup analyses further revealed that CYP9K1 overexpression followed a similar trend across countries, with no statistically significant differences observed between the countries (p > 0.05). This consistency suggests that the same CYP9K1-linked resistance mechanism may be spreading across different ecological and geographic regions, possibly through gene flow or shared selection pressure from insecticide use. These findings highlight CYP9K1 as a key metabolic marker conferring cross-resistance among Anopheles mosquitoes. The integration of CYP9K1 molecular surveillance into national vector control programs will strengthen early detection of resistance hotspots, inform insecticide rotation policies, and support the development of next-generation long-lasting insecticidal nets (LLINs) incorporating synergists or nonpyrethroid active ingredients. This evidence-based approach could guide tailored resistance management strategies essential for sustaining malaria control gains across sub-Saharan Africa.