Modelling the role of human and vector behavioural patterns on the persistent transmission of <i>Plasmodium falciparum</i> malaria in Nigeria

Abstract

Abstract Background Malaria, transmitted by female Anopheles mosquitoes, remains a major public health challenge in Nigeria, where approximately 97% of the population is at risk. Despite large-scale investments, Nigeria continues to bear the world’s highest malaria burden. Long-lasting insecticidal nets (LLINs) are central to prevention, yet their effectiveness is increasingly undermined by non-usage, delayed replacement, and growing outdoor biting activity. National surveys (MIS, PMI) consistently report gaps in LLIN use, irregular implementation of the three-year replacement strategy, and persistent outdoor biting. This study quantifies the relative contributions of these behavioural and entomological factors to sustained malaria transmission across five Nigerian states. Methods A deterministic compartmental model of malaria transmission was developed and calibrated using Bayesian inference with MCMC in CmdStanR. The model incorporated heterogeneous mosquito biting behaviour, LLIN effectiveness decay, and distribution cycles. Calibration used monthly malaria case data (2015-2024), demographic and entomological data (2015-2022), and DHS/MIS prevalence surveys (2015, 2018, 2021) for Akwa Ibom, Ebonyi, Kebbi, Oyo, and Plateau states. Counterfactual scenarios quantified malaria cases attributable to (i) outdoor mosquito biting, (ii) LLIN usage gaps, and (iii) delayed replacement. Parameter sweeps were used to assess how LLIN effectiveness changes with varying outdoor biting intensities. Results Eliminating outdoor biting yielded the largest reductions in malaria incidence—Akwa Ibom (82.4%, 95% CrI: 74.0-89.6), Ebonyi (92.0%, 95% CrI: 87.5-95.5), Kebbi (76.4%, 95% CrI: 51.0-92.6), and Oyo (83.0%, 95% CrI: 74.9-89.6). LLINs sub-stantially reduced malaria transmission only under low outdoor biting intensities—below 1 bite per mosquito per month in Akwa Ibom and Ebonyi, below 0.2 in Kebbi and up to 0.8 in Oyo. In Plateau, outdoor biting contributed minimally (5.8%, 95% CrI: 4.8-6.3), while the gap between LLIN ownership and use was the dominant factor (23.1%, 95% CrI: 22.5-23.8), rising to 36.5% (95% CrI: 35.5-37.6) when combined with delayed replacement. Conclusion Outdoor mosquito biting is a dominant driver of persistent malaria transmission in Akwa Ibom, Ebonyi, Kebbi, and Oyo states, whereas low LLIN usage is the leading factor in Plateau. Although maintaining high LLIN coverage, adherence, and timely replacement remains critical, these efforts alone are insufficient where outdoor biting is widespread. Strengthening Nigeria’s malaria control strategy will require integrating LLIN deployment with targeted outdoor vector control and state-specific behavioural interventions to achieve sustained reductions in malaria burden.