“…The latency period is the period during which an individual exposed to the disease can not pass it on to another individual. In the literature, several types of representation are presented, namely the introduction of an additional variable or the inclusion of a deviation in time: the discrete delay or the distributed delay (see [1,2,5,6,7,8,11,12,14,16,20,23,24,25,27,28]). Recently, considerable attention has been paid to model the relapse phenomenon, i.e.…”