Figure 3.

Influence of D₂ and D₄ on cholera traveling wave speeds when υ = 1, which is illustrated by plotting cholera traveling wave speeds as a function of a_i (i = 1, 2, 3). The base values of a₁, a₂ and a₃ are a₁ = 1.57 × 10⁻⁵ (day⁻¹), a₂ = 0.011 (person⁻¹·day⁻¹), and a₃ = 10 (cells · ml⁻¹·day⁻¹). For each plot, the upper solid curve refers to the progressive velocity c₊ and the lower dashed curve refers to the regressive velocity c₋. The curves in black (resp. red) show the critical cholera spreading speeds when D₂ = D₄ = 1 (resp. D₂ = D₄ = 10).