  In current paper, we put forward a reaction-diffusion system for West Nile
virus in spatial heterogeneous and time almost periodic environment with free
boundaries to investigate the influences of the habitat differences and
seasonal variations on the propagation of West Nile virus. The existence,
uniqueness and regularity estimates of the global solution for this disease
model are given. Focused on the effects of spatial heterogeneity and time
almost periodicity, we apply the principal Lyapunov exponent $\lambda(t)$ with
time $t$ to get the initial infected domain threshold $L^*$ to analyze the
long-time dynamical behaviors of the solution for this almost periodic West
Nile virus model and give the spreading-vanishing dichotomy regimes of the
disease. Especially, we prove that the solution for this West Nile virus model
converges to a time almost periodic function locally uniformly for $x$ in
$\mathbb R$ when the spreading occurs, which is driven by spatial differences
and seasonal recurrence. Moreover, the initial disease infected domain and the
front expanding rate have momentous impacts on the permanence and extinction of
the epidemic disease. Eventually, numerical simulations identify our
theoretical results.
