MODELING THE EFFECTS OF EXTERNAL PROTECTION MEASURES AND OPTIMAL CONTROL ON SEASONAL LASSA FEVER OUTBREAKS IN NIGERIA

Lassa fever, also referred to as Lassa hemorrhagic fever, is an endemic viral disease that frequently triggers epidemics in West Africa. This study presents a disease transmission dynamics model of Lassa fever that integrates external protective measures, the dynamics of rodent reproductive cycles, and the periodic nature of transmission from rodents to humans, aiming to provide a comprehensive understanding of the disease. The basic reproduction number $ \mathcal R_{0} $ can be deduced and as a threshold parameter for global dynamics. The disease-free periodic solution is globally asymptotically stable when $ \mathcal R_{0}<1 $, and the disease persists when $ \mathcal R_{0}>1 $. Based on the data provided by the Nigerian Center for Disease Control and Prevention, the Markov Chain Monte Carlo algorithm is used to simulate the model to find the baseline values of the unknown parameters and the exact value of $ \mathcal R_{0} $ is calculated as 1.6237. Next, the optimal control problem associated with the model is solved through the application of the Pontryagin maximum principle, implementing optimal control strategies for mitigating the transmission of Lassa fever virus. Finally, sensitivity analyses is conducted to determine the key parameters affecting the number of the infectious individuals. The findings suggest that enhancing the rate of external protection and optimizing protective efficiency have a substantial impact on the incidence of Lassa fever infections, serving as effective measures for disease control. However, these measures alone cannot completely eliminate disease transmission. If both measures to reduce rodent transmission and increase mortality rates are implemented, it will be possible to control the epidemic.