Can a healthy man with no open wounds or sores really contract HIV?
Yes he can, though the risk per act of vaginal sex is quite small under ordinary circumstances. The CDC estimates a chance of about 4 in 10,000 of contracting HIV this way. However, if either partner has another STD (herpes, chlamydia, gonorrhea, etc.) then the risk is substantially higher. Those diseases can compromise the integrity of the skin that lines the vagina, foreskin, and urethra, providing the virus with an easier path out of one body and into the other. And rough sex can also cause tears in those same tissues, also increasing the risk considerably. This increased risk from STDs and from violent sex is probably the main reason why sex workers and their clients are at high risk of contracting HIV in areas where the disease is common.