Influence of Physicochemical Characteristics and Heavy Metal Concentrations of Mosquito Breeding Sites on Malaria Vector Abundance in Isiala Ngwa North, Abia State, Nigeria

Abstract

Malaria remains a major public-health burden in Nigeria, yet local evidence linking breeding-site chemistry with malaria-vector abundance is limited. This study examined how physicochemical characteristics and heavy metal concentrations of mosquito breeding sites influence Anopheles vector abundance in Isiala Ngwa North, Abia State, Nigeria. An environmental-entomological survey was conducted using 48 breeding-site observations drawn from eight communities: Amapu Ntigha, Ihie, Mbawsi, Nsulu, Okpuala Ngwa, Umunna Nsulu, Umuode and Umuomainta. Three habitat types—drainage ditches, farm runoff channels and stagnant pools—were assessed across early and late rainy-season conditions. Anopheles larval abundance per 10 dips was quantified by combining Anopheles gambiae and Anopheles funestus counts. Water samples were analysed for temperature, pH, electrical conductivity, total dissolved solids, turbidity, biochemical oxygen demand, chemical oxygen demand, nitrate, phosphate and selected heavy metals. Descriptive statistics, habitat comparisons, Spearman’s rank correlation and negative binomial regression were used.A total of 1,764 Anopheles larvae was recorded across the ten-dip observations, with a mean abundance of 36.75. Farm runoff channels had the highest mean abundance (43.38), followed by drainage ditches (39.69) and stagnant pools (27.19). Sites sampled during the late rainy season recorded a higher mean abundance (41.75) than sites sampled during the early rainy season (31.75). Nsulu had the highest community mean (53.17), while Umuomainta had the lowest (26.33). Nitrate showed the strongest positive association with Anopheles abundance (Spearman’s rho = 0.565, p < 0.001) and remained significant in the adjusted negative binomial model (IRR = 1.65; 95% CI: 1.05–2.58; p = 0.029). Heavy metals were not significant predictors after adjustment. Nutrient enrichment, particularly nitrate contamination, appears to be a key environmental driver of malaria-vector productivity in the study area. The evidence supports integrated larval-source management and routine hydrochemical surveillance for malaria control.