A COUPLED SEIR-SIR FRAMEWORK MODELING SYNDEMIC DYNAMICS OF DIPTHTHERIA AND DENGUE OUTBREAKS: NONLINEAR AMPLIFICATION AND MULTISECTIORAL IMPLICATIONS IN NIGERIA

Abstract

This study presents a differential equation-based framework to model the synergistic effects of concurrent diphtheria and dengue fever outbreaks rrin Edo State, Nigeria. By integrating compartmental models (SEIR for diphtheria and SIR for dengue), we capture cross-disease dynamics influenced by shared health infrastructure, climatic conditions, and overlapping vulnerable populations. The mathematical model incorporates co-infection rates, delayed diagnosis, and healthcare saturation effects. Data from public health reports between January and May 2025 were fitted using parameter estimation techniques. Contour plots illustrate critical thresholds where interactions between outbreaks intensify disease burden, leading to nonlinear amplification of infection rates. Our findings emphasize the importance of a multisectoral response involving health, sanitation, education, and emergency services. The model also forecasts outbreak trajectories under various intervention scenarios, supporting evidence-based policy formulation. This study underscores the relevance of mathematical epidemiology in managing syndemic events and promotes integrated surveillance systems for effective public health response in sub-Saharan Africa.