Sexually transmitted diseases, besides HIV, include syphilis, which has an ulcer at one form, one stage of its development, and herpes simplex virus, which typically has several ulcers and is recurrent.  Other diseases that cause ulcers in the genital tract of both men and women exist.  All of those means that there's more chance that blood, and infected blood, can be transmitted and received from the infected individual.  So the solutions have included trying to reduce the chance for infections by treating the herpes simplex virus infection, treating syphilis for example, and even circumcision of adult uncircumcised men to reduce any chances of further infection along the foreskin or secondary infections along the head of the penis.  The end result is to reduce the chances of HIV by reducing the amount of raw wounds or ulcerations.  And it seems to help to do that.