Cost Effectiveness of Combined Long Lasting Insecticidal Nets Indoor Residual Spraying and Outdoor Residual Spraying for Zoonotic Malaria Control in Sabah Malaysia

Background Zoonotic malaria caused by Plasmodium knowlesi has emerged as the predominant malaria species in Malaysia, particularly in Sabah, where transmission occurs in forest-fringe environments involving macaque reservoirs and outdoor-biting mosquito vectors. Conventional malaria control strategies, such as long-lasting insecticide-treated nets (LLINs), may have reduced effectiveness in settings where vectors exhibit exophagic behavior. This study aimed to evaluate the cost-effectiveness of integrating LLINs with indoor residual spraying (IRS) and outdoor residual spraying (ORS) for zoonotic malaria control in Sabah, Malaysia. Methods A cost-effectiveness analysis was conducted to compare three intervention strategies: LLIN alone, LLIN combined with indoor residual spraying (LLIN + IRS), and LLIN combined with outdoor residual spraying (LLIN + ORS). The analysis was performed from the health system perspective using programmatic cost data and effectiveness estimates derived from available epidemiological evidence. Incremental cost-effectiveness ratios (ICERs) were calculated to estimate the additional cost per additional health outcome achieved when comparing integrated intervention strategies with LLIN alone. Results Both integrated strategies demonstrated improved effectiveness compared with LLIN alone. The LLIN + ORS strategy produced a lower incremental cost-effectiveness ratio compared with LLIN + IRS, indicating greater economic efficiency in achieving additional health benefits. These findings suggest that interventions targeting outdoor mosquito resting environments may better address transmission dynamics associated with zoonotic malaria in forest-fringe settings. Conclusion Integrating LLINs with residual spraying strategies can enhance malaria control in zoonotic transmission settings. In Sabah, the LLIN + ORS strategy appears to offer a more economically efficient approach compared with LLIN + IRS. Tailoring vector control strategies to local ecological and vector behavior characteristics may improve the effectiveness and efficiency of malaria control programs in regions affected by zoonotic malaria.