Fig 1. The schematic diagram for Model (1).

Susceptible humans can be infected from bites of an infectious mosquito, and susceptible mosquitoes can be infected from blood meals on an infectious person. The forces of infection, λ_*, are defined in Eq (4). After being infected, the susceptible individuals progress through the infectious states. Humans advance from the infectious state to the recovered state, while we assume that mosquitoes do not recover from an infection before dying.