The infectious rate, , controls the rate of spread which represents the probability of transmitting disease between a susceptible and an infectious individual. The incubation rate, , is the rate of latent individuals becoming infectious (average duration of incubation is 1/). Recovery rate, = 1/D, is determined by the average duration, D, of infection. For the SEIRS model, is the rate which recovered individuals return to the susceptible statue due to loss of immunity