Effect of explicit dynamics of free virus and intracellular delay

In this paper, based on quasi steady-state assumption, a phenomenological model of viral infections with intracellular delay is proposed to explore viral infection process. The existence as well as stability of equilibria and bifurcation are studied. The results indicate that the basic reproduction number is a sharp threshold parameter to determine the outcomes of infection when the intracellular delay is omitted. Otherwise, Hopf bifurcation may occur under some conditions. Combining with numerical simulations, we observe that the explicit dynamics of free virus can affect the dynamics behavior, the fluctuation scenario may appears in the case of full logistic proliferation term even if there is no intracellular delay. In addition, there are different patterns of bifurcation under different drug effectiveness and patient's age interacting with intracellular delay, which indicates that intracellular delay may induce complicated kinetics of virus infection.