Modelling the co-dynamics of alcohol abuse and HCV transmission with integrated intervention strategies

Heavy and harmful alcohol use is increasingly recognized as a key cofactor in hepatitis C virus (HCV) transmission and in the progression of HCV-related liver disease. We develop and analyse a coupled alcohol-HCV transmission model that links escalation to heavy drinking, treatment and relapse with staged HCV infection, spontaneous clearance, antiviral treatment, and waning immunity. The model explicitly captures bidirectional feedbacks between alcohol abuse dynamics and HCV transmission, allowing the assessment of both alcohol-focused and infection-focused interventions within a unified mathematical framework. The model is shown to be mathematically well posed, and an explicit basic reproduction number is derived, providing a clear threshold for HCV persistence or elimination in the presence of alcohol-induced risk heterogeneity. Numerical simulations show that alcohol-only measures yield limited reductions in long-term HCV burden, while treatment scale-up alone leaves substantial residual transmission when heavy drinking remains high. By contrast, integrated intervention strategies that simultaneously reduce heavy drinking and expand access to antiviral therapy produce synergistic effects, leading to markedly larger and more sustained declines in chronic HCV prevalence. These findings highlight the limitations of single-sector approaches and demonstrate that coordinated alcohol harm-reduction and HCV treatment strategies substantially enhance prospects for long-term disease control and elimination.