No anxieties here, just some Qs I've been trying to scour the internet to get answered; but after going through the forum and some dubious information online, I've decided to just go ahead and ask here for max benefit:

1) You've repeatedly mentioned that oral carries negligible to no risk of HIV transmission, however, my question here is how does infection actually happen?  (In terms of mechanisms and/or scenarios) Am I correct in understanding that it should involve infected semen/secretions coming into contact with open cuts/sores/lesions/bleeding gums inside the mouth?

2) You've also repeatedly mentioned that mutual masturbation/frottage is also little to no risk of HIV transmission; but what if (between two gay males) the urethra openings are in direct contact with each other and there was an exchange of fluids? Is the risk still the same or higher?

3) I've been desperately trying to find an answer for this one: Hypothetically speaking, if I am on PrEP and have unprotected sex with an HIV+ male with a high viral load, how long does HIV live inside my body before my immune system wipes it out? Dr. Handsfield previously replied that this was 'very complex, could be weeks/years', but I'd very much appreciate a detailed reply to this particular question!

4) I know by now that the risk is little to 0, but I have a tiny friction burn on my penis as a result of injury from masturbation - is this burn considered exposed mucuous membrane that can act as a potential track towards infection if my partner performs unprotected oral sex on me? Should I wait for it to heal before going back to having sex?

Many, many thanks as always. Very grateful for all your time and efforts.

Welcome back. Directly to your questions. But you're asking very hypothetical questions. The fact is that HIV infection is inefficient and the large majority of exposures do not result in transmission. The biological reasons aren't completely understood, but I don't see that they are important. If transmission doesn't occur, who cares why?

1) For infection to take hold, large amounts of HIV (not just a few viruses) need to access particular cells primarily located in deep tissues or in the bloodsrream. This can happen through various mechanisms, but in general oral sex doesn't provide them.

2) Could infection occur in the scenario you describe? Probably yes, bu very rarely.

3) Your immune system might never "wipe it out". But HIV itself is fragile and probably doesn't live long. There is no such thing as acquiring HIV in the body an infection/invasion not happening until sometime later. If infection doesn't take hold right away, it never does -- as far as we know.

4) Oral sex is always low risk:  there has never been a scientifically documented case of HIV transmission from the mouth or oral sex. Among other things, saliva kills HIV -- although other mechanisms also may explain the low risk. That said, common sense says to not push your luck and not have oral sex (or any other sex) when opens sores might be exposed. But probably there would be no risk even if you were to ignore this advice.

Thanks for the thanks in advance. I hope these replies are helpful.

HHH, MD

May I please trouble you with another elaborate answer and additional details? Just to avoid any potential misunderstanding, I do not mean on the super rare occassions where PrEP fails, just the presence of the virus itself inside the body of a PrEP user without being able to infect - so if the immune system doesn't wipe it out, and it can't replicate inside the cells and start an infection, what happens to the virus then?

I saw a YouTube video recently that explained how PrEP stops the virus from replicating inside specific immune cells and thus dies out because it can't replicate and spread - but I would rather understand the mechanism directly from you in lay terms.

Thanks again and apologies for my late reply - thanks for keeping the thread open and hope you had a good weekend Doctor.

It is not possible to acquire HIV, or to transmit it to another person, without being infected and developing a positive blood test. I cannot comment on what you saw on YouTube, but you describe a logical biological mechanism to explain PEP/PrEP failure. However, in that situation the virus could not be transmitted to another person until the drug(s) are gone from the body and viral replication could start (or resume). Transmission requires millions or billions of viruses, which also need to spread to transmissible compartments, such as semen or other body fluids. Small amounts of virus are insufficient for transmission. If PEP or PrEP fails, that person would not be infectious until at least a week or two after completing treatment.

Does that get to your point? The take-home message is that someone on PEP (or on PrEP if treatment continues after one is exposed) is not infectious to others while taking the drug, and probably not until at least a week or two after completing treatment. 

One last question: So does that mean a PrEP/PEP user with traces of the virus in their system (enough to infect) needs to keep on taking PrEP/PEP for life in order to prevent the virus from replicating and infecting? Even if the drugs are continued for 2 weeks after the last exposure, this is NOT a guarantee that infection won't or can't take place, correct?

That completes this thread. I hope the discussion has been helpful.