Fig. 2
From: The effect of men who have sex with men (MSM) on the spread of sexually transmitted infections
Network diagram among eight types of infection states. The red arrows represent the type-reproduction numbers of all sexual (horizontal) transmission events that occur between subpopulations. The blue arrows indicate the type-reproduction numbers of all mother-to-child (vertical) transmission events caused by infected women. The thin arrows indicate that the contribution is small when the proportion of homosexual individuals is small (see Table 3)