PERMANENCE AND EXTINCTION OF A NON-AUTONOMOUS HIV-1 MODEL WITH TIME DELAYS.

The environment of HIV-1 infection and treatment could be non- periodically time-varying. The purposes of this paper are to investigate the effects of time-dependent coefficients on the dynamics of a non-autonomous and non-periodic HIV-1 infection model with two delays, and to provide explicit estimates of the lower and upper bounds of the viral load. We established sufficient conditions for the permanence and extinction of the non-autonomous system based on two positive constants R^* and R_* (R^* ≥ R_*) that could be precisely expressed by the coefficients of the system: (i) If R^* < 1, then the infection-free steady state is globally attracting; (ii) if R_* > 1, then the system is permanent. When the system is permanent, we further obtained detailed estimates of both the lower and upper bounds of the viral load. The results show that both R^* and R_* reduce to the basic reproduction ratio of the corresponding autonomous model when all the coefficients become constants. Numerical simulations have been performed to verify/extend our analytical results. We also provided some numerical results showing that both permanence and extinction are possible when R_* < 1 < R^* holds. [ABSTRACT FROM AUTHOR]