Fig. 1.

A diagrammatical representation of the model. The boxes represent the different classes, and arrows indicate transitions between the different classes. In a well mixed population the ensemble means of the stochastic model obey the differential equations (14): dS/dt = αR + ΨX - βS(I + Y)/N, dI/dt = βS(I/N) - γI, dR/dt = γ(I + Y) - αR, dY/dt = β(1 - ε)S(Y/N) - γY, dX/dt = βεS(Y/N) - ΨX.