Figure 2. . Evolution of HIV virulence in a steady state host population of 10,000. There are two HIV strains in these simulations. For one, the asymptomatic periods is 520 weeks and, in the more virulent population (*), it is 260 weeks. The duration of stages 0,1, and 3 is identical for both populations and the same as those in Figure 1. A) The weekly rates of transmission of the virus are identical in both populations, so that during the asymptomatic period in a wholly susceptible host population, the more virulent strain of HIV is responsible for 0.5 rather than 1 secondary infection, R02* = 0.5, while R01 = 1.0. The remaining R0s of these two populations are identical to those in Figure 1. B) Early transmission in the more virulent strain is greater than that in the less virulent, R01* = 1.05, while R01 = 1.0 secondary infections. The weekly rates of transmission of are same for rest of the stages, R00* = R00 =0, R02* = 0.5, R02 = 1, and R03 * = R03 = 1.