An epidemiological model with arbitrary distributions for infection and relapse stages

In low tuberculosis (TB) burden settings, recurrent tuberculosis is predominantly driven by relapse. Relapse, defined as the recurrence or re-emergence of a disease or condition after a period of remission or apparent recovery, poses a significant global public health challenge. The variability in the duration of infection and relapse stages among individuals calls for a rigorous mathematical framework to evaluate the impact of this heterogeneity on disease transmission dynamics. To address this, we develop a general integral equation model tailored to low TB burden settings, incorporating arbitrary distributions for the infection and relapse stages, thereby capturing individual variations in sojourn times during disease progression. Our analysis focuses on the existence and stability of equilibrium solutions, which depend on whether the basic reproduction number is less than or greater than one. Additionally, we investigate the reformulation of the integral model into an ordinary differential equation system by assuming exponential or gamma distributions for the sojourn time durations, potentially facilitating further theoretical analysis and numerical computations.