STATIONARITY AND PERIODICITY OF POSITIVE SOLUTIONS TO STOCHASTIC SEIR EPIDEMIC MODELS WITH DISTRIBUTED DELAY

摘要

In this paper, we consider two SEIR epidemic models with distributed delay in random environments. First of all, by constructing a suitable stochastic Lyapunov function, we obtain the existence of stationarity of the positive solution to the stochastic autonomous system. Then we establish sufficient conditions for extinction of the disease. Finally, by using Khasminskii's theory of periodic solutions, we prove that the stochastic nonautonomous epidemic model admits at least one nontrivial positive T-periodic solution under a simple condition.