[Question #6266] PReP oral sex and oral HSV2

17 months ago
Hello and thank you for this excellent service. 
1- I recently read a study on pubmed titled ‘Expert consensus statement on the science of HIV in the context of criminal law’, this was published in 2018 and included multiple international HIV experts. In section 2.3.1 the collective statement is that if a HIV negative person that is on PReP performs oral sex on a hiv positive male, there is no possibility of HIV transmission. Do you agree with this statement? Other reputable websites agree (eg. the body.com), yet some other websites stop short of stating ‘no possibility’ and instead state ’very low possibility’. I already know that oral sex without PReP is already a very, very low risk (approx. 1/10,000). If a HIV negative person is on PReP and takes it correctly (daily), can he be certain HIV transmission will not occur if the only act will be oral sex, including swallowing semen? In this scenario there will be no anal-genital contact at all. Also would your assessment change if there were minor cuts or abrasions in the mouth?2 - I want to know the per act chance of acquiring oral HSV2, due to performing oral sex on a male. I know that there is no existing research to indicate a specific figure, but if you could please give me a per act figure based on your expert knowledge and experience. The following details below may assist you in determining a per act figure. I am be travelling to an area with higher than average STD rates, I will likely participate in MSM oral sex only.- I will be taking Doxycycline 100mg daily (as an anti-malarial tablet).- I already have oral HSV1 cold sores (I believe this provides some immunity against HSV2).- I am taking PReP (Based on some research I have read, Tenofovir can help prevent HSV2 acquisition). Taking the above information into account, what are my per act chances or acquiring oral HSV2? I do have a follow up question as well. Thank you. 
Edward W. Hook M.D.
Edward W. Hook M.D.
17 months ago

Welcome to the Forum and thanks for your detailed questions.  I'll do my best to answer your questions although as you have already noted, my responses regarding HSV-2 and risk for infection will be speculative as their are no data on this subject.

Regarding variation in guidelines, the variability as to whether PrEP would make oral sex with swallowing of ejaculate a no risk or "just" an extraordinarily low risk event is more a reflection of your web sites and the organizations attitudes as to whether one can ever say "never".  Science continues to search for new knowledge and new observations of previously undescribed events occur every day.  Further, every statistical statement is an estimate since very, very rare events might happen the next time an observation is made.  We know that properly taken PrEP reduces risk for acquisition of HIV to close to zero, we know that even among other men with male sex partners, most persons will not have HIV, and we conservatively calculate the risk of acquiring HIV from performance of fellatio on an infected person who is not on therapy is less (and probably far less) than 1 in 10,000.  Putting these together the risk for infection is i in many millions.  That is not zero but is becomes so low that it cannot be effectively calculated.  The analogy I have used on this Forum is that the risk associated with the hypothetical situation you describe is likely (who really knows) as low or lower than your risk for being hit by a meteor falling from the sky.  Abrasions on the mouth or oral HSV-1 would not meaningfully change this estimate.

As for risk for acquisition of HSV-2, this subject is has been far less exhaustively studied than the risk for HIV discussed above.  We know that when oral herpes is diagnosed, less than 1% is due to HSV-2, that even most exposures to infected persons (even in the presence of lesions) does not result in infection, and that HSV-1 does confer a modest degree of protection from acquisition of HSV-2.  Putting this together, my estimate is that your risk for infection would be lower than 1 in a million and probably substantially lower.  I cannot be more precise than that.

I hope these comments are helpful to you.  EWH

17 months ago
Hello Dr Hook and thank you for your prompt response.  Your assistance is greatly appreciated! Just to give you some background, I am a 35yr old bisexual male, I am taking PReP because my long term female partner is HIV positive, and she does not yet have an undetectable viral load.  I have a quite a few questions, so I apologise in advance for any inconvenience. This service is one of a kind and I am taking the opportunity to ask multiple questions. I hope that is ok.
1 - I think I understand what you mean in the sense that in science 'zero' can never be truly achieved. I.e. Paracetamol has been fatal in very rare occasions, yet the millions of times it is used, this does not usually occur, thus according to science Paracetamol itself cannot be considered 100% safe. Is that what you mean regarding zero risk being non-existent in science? In my case of performing receptive oral sex whilst on PReP, would you agree that there is no measurable risk of HIV transmission? Would you agree that there is no need at all to be concerned about HIV transmission following this act? 
2 - Is PReP active against HIV-2? I know HIV-2 is usually isolated in West African nations, however if exposed, would PReP be just as effective as HIV-2? There are probably no studies to confirm this, but if you could please provide an answer based on your experience and knowledge as an STD expert.
3 - Does Ceftriaxone IMI and Azithromycin interact with Benzathine Penicillin IMI? If I happen to acquire Syphilis and Gonorrhea, can I safely receive the first line of treatment for both STI's? Or will the Benzathine Penicillin be changed to Doxycycline? 
4 - I will be taking 100mg of Doxycycline (for anti-malaria) during the time the sexual contact will occur, will this prevent any bacterial STI acquisition? 
5 - If my partners reaches an undetectable viral load and I decide to stop PReP, how long should I continue to take it from the last exposure? Eg. if my last exposure was today, and I want to stop taking PReP, when should I stop taking it? When will a HIV test be conclusive after stopping PReP? Using the example of my last exposure being today, from when I stop taking PReP, when can I get a conclusive HIV test?
6 - Will taking Valacyclovir daily help to prevent oral HSV2 acquisition? I could not find any research on this, except 1 study that mentioned HIV-positive men using Valacyclovir as a prophylaxis to HSV2. In your expert opinion, do you think that taking Valacyclovir daily can reduce oral HSV2 acquisition?
7 - If I acquire oral HSV2, is it possible I will infect my children through normal parental contact (kiss on check, playful light kiss on lips, sharing utensils)? Also, what about infecting my long term female partner? We are not incredible sexually active, sex occurs probably monthly and cunnilingus rarely occurs. Some people have described oral HSV2 as virtually non-infectious to others would you agree? If I acquire oral HSV2, should I be concerned about infecting others? Or should I just carry on with my life as usual?

Edward W. Hook M.D.
Edward W. Hook M.D.
17 months ago

I'll try to answer your questions briefly but we have to limit the extent of our replies.  Many of these questions would be more appropriately discussed with your own health care provider:

1.  Your summary is correct.  I would have little concern about performing oral sex on an infected partner.  I would add that if you are talking about performing oral sex on your HIV+ female partner, your risk of infection is likely lower than for performing fellatio on an infected male partner. 

2.  HIV-2 is so rare that there are few data on its utility vs HIV-2.  I can think of no reason why PrEP would not also prevent HIV-2, as well as HIV-1. 

3.  There are no interactions between ceftriaxone/azithromycin for gonorrhea and benzathine penicillin for syphilis. If you happened to acquire both infections at the same time your could be treated with both first line therapies.

4.  Yes, doxycycline would likely prevent chlamydia and syphilis most likely.

5.  There are no data on when it would be safe to stop taking PrEP. Further, it is possible that achievement of an undetectable viral load is a process rather than an event and there could, conceivably be intermittent viral shedding as the infected person becomes undetectable.  Out of an abundance of caution, I would want at least two undetectable viral loads OR at least two weeks to past before stopping PrEP.  Once off PrEP a 4th generation HIV test would be reliable 6 weeks after the last exposure

6. There are no studies of valaciclovir for prevention of HSV acquisition, 

7. Oral HSV-2 is so rare that there are no data to answer the question you are asking.  I would assume that you are not likely to be infectious through the sort of casual contact you describe.  I would avoid kissing persons if an oral lesion is present.


17 months ago
Thank you Dr Hook. 
This is my last post, I would like clarification on 3 things and I will ask 1 final question.
1 - by performing fellatio, anilingus or cunnilingus, including swallowing ejaculate/vaginal/anal secretions, whilst on PReP, HIV acquisition is realistically not possible and there is need for concern from a medical perspective. Is this correct?
2 - the possibility of acquiring oral HSV2 by performance of fellatio/anilingus/cunnilingus is incredibly low, lower than 1 in a million and probably substantially lower. Is this correct?
3 - oral HSV2 sheds very rarely and is not spread through casual kissing on lips/cheeks. With no lesions present, I should not be concerned about infecting others through oral sex/kissing, is this correct? I would obviously avoid such contact if lesions are present.
Final question - If I engage in anal sex as the insertive partner, and I am on PReP and I use a condom correctly, what is the per act chance of acquiring genital HSV2? If you could please provide an estimate for this act, that would be great. 
Otherwise, thank you for providing this service. I wish you a long and healthy life! All the best!
Edward W. Hook M.D.
Edward W. Hook M.D.
17 months ago

These questions are a bit repetitive  Repeating the questions will not change the answers.

1.  Agree.  FYI, if not on PrEP there is a likely hierarchy in which fellatio is a higher risk than either cunnilingus of analingus. With PrEP risk should be virtually non-existent.

2.  There are just no data to provide a quantitative answer.  Risk if very, very low.

3.  Correct

4. (new question.  Again, no data to provide a quantitative answer.  Very, very low

Thanks for your thanks.  As you note, this thread will now be closed.  EWH