Figure 15. The number of human cases with time under the situation that there exists human-to-human transmission when migrant birds are viewed as the original infection source.

(a) β_hh = 5 × 10⁻⁹, β₁ = 4.612 × 10⁻⁸, β₂ = 8.2 × 10⁻¹⁶; (b) β_hh = 10 × 10⁻⁹, β₁ = 5.728 × 10⁻⁸, β₂ = 1.2 × 10⁻¹⁶. p = 1.7.