If alphas are into sexual conquering and having as much sex as possible with as many partners as possible doesn’t that incur a higher risk of contracting STIs?

I’m sure that’s probably true. I don’t think the risk of HIV is very high at all, but Alphas certainly get STIs like gonorrhea, herpes, or chlamydia. 

Life is not risk free. Alphas choose to accept the risk in order to live life on their own terms. I can’t say I blame them.