No worries. It is not realstic to suspect the nipples had been previously used. But even if they had, there would be no risk for the reasons listed by curiosityb.
I'm worried about your emotional status. If these replies clear things up for you and you are able to feed your baby without worry, that would be great. If not, consider professional counseling. These are not rational thoughts. Sorry to be so blunt, but that's the way I see it. I have only your wellbeing in mind, and your baby's.
not just boiling, air kills hiv. hiv can't live outside of human's body. if that was a risk whole world could be infected. it only spreads through nursing a child when baby drinks tons of breast milk for weeks. no risk.