A co-infection model for HPV and syphilis with optimal control and cost-effectiveness analysis
Abstract
A co-infection model for human papillomavirus (HPV) and syphilis with cost-effectiveness optimal control analysis is developed and presented. The full co-infection model is shown to undergo the phenomenon of backward bifurcation when a certain condition is satisfied. The global asymptotic stability of the disease-free equilibrium of the full model is shown not to exist when the associated reproduction number is less than unity. The existence of endemic equilibrium of the syphilis-only sub-model is shown to exist and the global asymptotic stability of the disease-free and endemic equilibria of the syphilis-only sub-model was established, for a special case. Sensitivity analysis is also carried out on the parameters of the model. Using the syphilis associated reproduction number, ℛ0s, as the response function, it is observed that the five-ranked parameters that drive the dynamics of the co-infection model are the demographic parameter μ, the effective contact rate for syphilis transmission, βs, the progression rate to late stage of syphilis σ2, and syphilis treatment rates: τ1 and τ2 for co-infected individuals in compartments Hi and Hl, respectively. Moreover, when the HPV associated reproduction number, ℛ0h, is used as the response function, the five most dominant parameters that drive the dynamics of the model are the demographic parameter μ, the effective contact rate for HPV transmission, βh, the fraction of HPV infected who develop persistent HPV ρ1, the fraction of individuals vaccinated against incident HPV infection ϕ and the HPV vaccine efficacy πh. Numerical simulations of the optimal control model showed that the optimal control strategy which implements syphilis treatment controls for singly infected individuals is the most cost-effective of all the control strategies in reducing the burden of HPV and syphilis co-infections.
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