is the basic reproduction number for HEV. The term s mzs is the proportion of the exposed humans that survive the incubation period. The other fraction, br(1{l)(1{b) mzc is transmission rate of HEV during the infectious period of the human. The disease-free equilibrium point is stable if R 0 v1 (see Supporting Information S1) When R 0 w1 the endemic equilibrium point in equation (8) exists and is stable. This equilibrium is attained via oscillatory dynamics, with period T*2p