For example, consider a mosquito-borne disease where humans infect two mosquitoes, while mosquitoes infect three humans, as shown in Figure 1 . For convenience, label these R H = 2 and R M = 3. Then the number of humans infected from a primary human (via mosquitoes) is R 0 = 2 × 3 = 6. (This is also the value calculated by the survival function.)