Table 1.

Model parameters and their definitions

Parameter	Definition
$\delta$	Birth (and death) rate of hosts
$\mu$	Loss of immunity rate
${\alpha }_1$	Infectivity rate, first infectious stage
${\alpha }_2$	Infectivity rate, second infectious stage
${\nu }_1$	Rate of progression from first to second infectious stages
${\nu }_2$	Recovery rate, only from second infectious stage