“…Epidemic models such as (2.6) with an arbitrarily distributed exposed stage have been studied in the literature; see, for example, [8,14,15]. Recently, a model of this type, but including the possibility of disease relapse, has been proposed in [40,43] to study the transmission and spread of some infectious disease such as herpes, and its global dynamics have been completely investigated in [31,40]. The model in [31,40,43] can be regarded as a generalization of our model (2.6), and thus the stability results there can be immediately applied to our model (2.6) by setting the relapse rate to zero.…”