  An epidemic model, where the dispersal is approximated by nonlocal diffusion
operator and spatial domain has one ?xed boundary and one free boundary, is
considered in this paper. Firstly, using some elementary analysis instead of
variational characterization, we show the existence and asymptotic behaviors of
the principal eigenvalue of a cooperative system which can be used to
characterize more epidemic models, not just ours. Then we study the existence,
uniqueness and stability of a related steady state problem. Finally, we obtain
a rather complete understanding for long time behaviors, spreading-vanishing
dichotomy, criteria for spreading and vanishing, and spreading speed.
Particularly, we prove that the asymptotic spreading speed of solution
component (u; v) is equal to the spreading speed of free boundary which is
?nite if and only if a threshold condition holds for kernel functions.
