Aids can be transmitted through things such as contact with blood, IV, blood transfusion.
Or even slaughtering Amekelites, huh? There's no need at all to think that the anti-sex rules in Deuteronomy had anything to do with health. They were for keeping the desired social order the way it was - "don't mess with my wife, and maybe I won't mess with yours."
Not strictly on topic, perhaps, but the OT would not have been too concerned about at least some of those ailments. Syphilis was apparently confined to the Americas before Columbus, and AIDS didn't jump to humans until perhaps the 1940's.
Given that the vast majority of aids infections are MSM
MSM=??, Buz? Male/male sex? That's not even cause of a simple majority of AIDS cases in this century. In the 80's in the US it was, but that isn't now.