This thead reminded me of a question I have always wondered - how does the HIV virus get from person A to person B.
Easy to understand for injecting drug users - infected blood is directly injected into the bloodstream.
Easy to understand for anal sex, for the ‘recipient’ - infected semen may enter small cuts or abrasions in the rectum.
Even understandable in vaginal sex for the same reason.
But what about for the …um…‘provider’ of said semen in both vaginal and anal sex? Unless the penis has cuts on it how could the virus possibly pass through the skin? It is just like if someone bled onto your skin who was infected. My understanding was that the virus does not pass through the skin.
In a situation like this the issue is that normal skin is different from mucous membranes. A lot can pass through mucous membrane that cannot pass through normal skin. This may not be the whole answer but I hope it makes thing a little clearer.
It would also seem that the urethral mucosa provides an easier route to the bloodstream of the man than the skin on the outside of the penis, and that may also come in contact with HIV that the female or the male is carrying. Or, vice versa, actually. If you can get that buring sensation from soaping up too vigorously in the shower, then it can’t be too hard for microbes to make their way into that same viciinity.
No cite, but I’ve heard that female-to-male vaginal transmission is the most unlikely route of infection. It still happens, of course, but it’s a lot rarer than other avenues since the tiny tears on the penis have to connect with tiny tears on the vagina to make infection possible. Same goes for anal sex where the receiver is the infected partner, though I think it’s more likely in that case since there are more tears and places where the blood can get through.
In the case of vaginal sexual intercourse, barring direct blood-semen contact through some sort of lesion, the most importasnt route of infection is through a class of antigen-presenting cells referred to as dendritic cells (commonly known as Langerhans cells), which reside in genital epithelia (esp. cervical and vaginal mucosa). These cells present a variety of receptors for HIV binding, and their job is to move foreign proteins quickly from where they are encountered to where they can be presented to the immune system, by migrating from the epidermis to the lymph nodes. The cells are not lysed by HIV infection like T-Cells, but still can harbor the virus and allow its replication. As such, they provide an insidiously efficient route of entry, a sort of Trojan Horse, delivering a concentration of virus to more of the very sorts of cells it infects.