Assessing the Influence of Silicosis Infection on Tuberculosis Development and Persistence

Beyond human immunodeficiency virus (HIV), silicosis is recognized as a major risk factor for tuberculosis (TB), particularly among mine workers exposed to respirable crystalline silica. Silicosis is an incurable pneumoconiosis caused by the inhalation and deposition of fine silica particles in the lungs. In this study, we develop, for the first time, a TB–silicosis coinfection model to assess the impact of silica dust inhalation on TB transmission dynamics. Without accounting for silicosis infection, we determine a threshold that ensures the global elimination of TB. The coinfection model inherits the backward bifurcation property of the TB-only submodel, in the sense that when the basic reproduction number R0 is less than one, a stable endemic equilibrium coexists with the disease-free equilibrium (DFE), thereby complicating TB elimination efforts. Sensitivity analysis further suggests that, regardless of vaccination coverage or efficacy, sustained silica exposure will maintain TB persistence and even preclude local disease control. Numerical simulations are carried out using a nonstandard finite difference (NSFD) scheme, which is dynamically consistent with respect to the qualitative properties, including the positivity, boundedness, and stability of the DFE of the continuous model. The obtained results indicate that reducing the silicosis progression rate mitigates TB prevalence as well. Additionally, mining recruitment and silica dust shed in the air are important drivers of the coinfection dynamics of TB–silicosis, recommending the implementation of interventions aimed at reducing human exposure to high-risk mining environments (e.g., drilling, blasting, and crushing) through mechanization and automation. Conversely, enhancing silica dust removal significantly reduces the prevalence of silicosis and TB–silicosis coinfection, underscoring the critical role of effective dust control strategies, including the implementation of improved ventilation systems and wet dust suppression techniques to limit exposure to respirable silica dust, thereby lowering the risk of silicosis and contributing to TB control.