Figure 2.

Moments of the stochastic model, shown as the mean number of infective hosts (solid curve) and mean ± s.d. (dashed curves), calculated using the moment equations. For comparison, numerical estimates of these quantities, obtained by averaging over 10 000 simulation runs of the stochastic model, are shown by the symbols. The initial condition has five infective hosts and five infective vectors. Parameter values are as follows: p=0.2; q=0.15; k=0.5; ξ=δ=1/7; H=100; and V=1000. The simulation-based estimates of moments are only calculated over realizations in which the infection has not undergone extinction by the time of interest (i.e. they are moments conditional on non-extinction). For the parameter values employed, extinction occurred in less than 2% of simulation runs.