Welcome to the forum. Directly to your questions.
1) HIV transmission is a very complex event, biologically speaking. The susceptible cells typically are internal, and even if enough virus can arriive at those sites -- which typically are protected by physical, chemical, and immunologic barriers -- then it generally still takes lots of virus to initiate infection. Certainly a single virus could do it, but the odds are overwhelmingly against it. In a way it's like fertilization. You've probably seen those films of myriads of sperm trying to get inside the ovum; only one makes it. That's why men with sperm counts of "only" a few million per ml usually are infertile. Or to look at it another way: maybe only a single virus needs to get into the right kind of cell -- but the odds of that virus contacting that cell are so low that millions and millions of viral particles have to be placed in the vicinity for the odds to favor infection. That's why even the highest risk sexual exposure -- desposition of infected semen into the rectum -- has an average infection rate of only 1 in 200 exposures.
2) HIV is very fragile; it litereally falls apart. Saliva speeds up that process. Once exposed to saliva; the virus is destroyed and cannot infect. I don't know the biological mechanism of saliva's activity against HIV, but my guess is that it involves the digestive vaccines in saliva. As suggested in your last question, it probably dissolves the outer membrane of the virus.
3) Probably blood mixed with saliva would be quickly rendered non-infectious -- but I don't know if such an experiment has actually been done.
4) Vaccines work by stimulating the immune system. Simply having some sort of chemical reaction or enzyme in saliva that inactivates HIV doesn't mean you can make a vaccine with the same capability.
5) Correct. Once inactivated by saliva, the virus is dead as a doornail. For most viruses, if the outer membrane is destroyed, the virus cannot survive, replicate, or infect.
You don't describe the exposure(s) that concern you, if any. As you will see in most questions on this forum, we generally don't deal with the biological explanations. The fact is that, whatever the reasons, exposure to saliva -- and therefore oral sex -- carries little or no risk for HIV transmission. The biological reasons for it really don't matter.
Regards-- HHH, MD
Thanks for the comprehensive answers and i apologize, i didnt know this site doesn't get into biological explanation. I am a male and had a risk via oral sex (from female CSW) last year but already tested negative. Since then, i am interested in studying more about HIV. I then search this site for more information about HIV transmission. I found it very surprising that the rate of infection is low , even for unprotected sex anal/vagina. I always thought its a one time exposure w/ one virus then jackpot.
it sounds like the HIV virus does not get to pick which cell it infects? Can HIV virus infect any cell to cause infection or only white blood cell?
I think i get the idea now. Because during sex(any sex) virus has to break through layers of barriers before it can infect the cell, thats why the rate is so low? Then injection drug is directly into blood stream so the rate is higher?
Thanks again for the assistance.
The only cells in the body that are susceptible to HIV are those that have proteins on their surface called CD4 and CCR5. Only a few kinds of cells have those characteristics, specifically certain lymphocytes (not all of them), macrophages, and a few others. Most white blood cells are not susceptible.
Injection of HIV infected blood into the bloodstream is the only near-certain route of HIV transmission, about 90% of people who receive a transfusion with HIV infected blood.
Here is another thread that discussed the biology of HIV/STD transmission. Start reading with the follow-up comment dated December 14: http://www.medhelp.org/posts/show/1119533
That will end this thread. If you need more detail than this, I suggest more sophisticated research via the web or a medical library. The bottom line remains that receiving oral sex carrlies little or no risk for HIV (truly no risk, according to some experts).
Thanks for all the information. That helped me greatly. One last question if you dont mind. When i took the rapid test last time, they used a exposed blade finger prick device (it was all white) opposed to the normal spring loaded units i am familiar with. I did however see the nurse grab one out of the box and kinda twisted it open. The result came back negative. I assume i have nothing to worry about the exposed blade finger prick device either being containmented or re-used ?
Oh come on. Of course not. You assume correctly. No more comments on this thread.