A semigroup approach to the study of a general stochastic epidemic

A general stochastic epidemic, with immigration, in a large population is examined, introducing exponentially distributed latent and incubation periods. By means of semigroups, existence and uniqueness are proved for the solution of the initial-value problem arising from the stochastic model proposed. Equations for expected values of the random variables describing the epidemic are derived rigorously from the Kolmogorov equations of the process. Conditions for the extinction of the epidemic are also obtained.