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Wondering about something
I have been wondering for a long time why there is such a small risk of contracting HIV from one sexual act. Is it that things have to be just right for it to occur or is it the repetitive nature of the act that causes another to catch it?
MEDICAL PROFESSIONAL
Although this is a thread jump, it raises a question on lots of users' minds, so here's a response that may resolve a lot of confusion.
The recent research about most HIV infections starting from a single virus particle is understandably confusing. But it's really pretty simple. For that single virus to initiate INFECTION by getting into just the right place requires EXPOSURE to millions or billions of virus particles.
It's sort of like conception, sperm counts, and fertility. It only takes one sperm to fertilize a human egg, but the egg is actually pretty resistant to entry by sperm. Only one of thousands or millions of sperm that contact the surface of the ovum actually makes it inside. That's why normal sperm countsare 20-100 million per milliliter of semen, and guys with sperm counts of "only" 5 million are usually infertile. (This analogy is intended only as a numerical example. The biology of sperm entry and HIV infection are enitrely different.)
See the following thread, and start reading with the follow-up comment dated December 14. In reading it, keep in mind that the single viral particle that is "lucky" enough to get into a place that allows replication requires EXPOSURE to large amounts of virus: http://www.medhelp.org/posts/show/1119533
The recent research about most HIV infections starting from a single virus particle is understandably confusing. But it's really pretty simple. For that single virus to initiate INFECTION by getting into just the right place requires EXPOSURE to millions or billions of virus particles.
It's sort of like conception, sperm counts, and fertility. It only takes one sperm to fertilize a human egg, but the egg is actually pretty resistant to entry by sperm. Only one of thousands or millions of sperm that contact the surface of the ovum actually makes it inside. That's why normal sperm countsare 20-100 million per milliliter of semen, and guys with sperm counts of "only" 5 million are usually infertile. (This analogy is intended only as a numerical example. The biology of sperm entry and HIV infection are enitrely different.)
See the following thread, and start reading with the follow-up comment dated December 14. In reading it, keep in mind that the single viral particle that is "lucky" enough to get into a place that allows replication requires EXPOSURE to large amounts of virus: http://www.medhelp.org/posts/show/1119533
MEDICAL PROFESSIONAL
Welcome the forum.
The first reason is the correct one. HIV simply is inefficiently transmitted, so it is statistically unlikely that there will be sufficient virus exposure for any one sexual event. For anal sex without a condom, from an infected insertive partner (top) the chance of transmission to the receptive partner (bottom) averages somewhere around once for every 100-200 exposures. In the opposite direction, if the anal partner is infected, it averages somewhere around 1 chance in 500. For unprotected vaginal sex, it's around 1 in 1,000 to 2,000 per exposure. For oral it's 1 in 10,000 to 1 in 20,000 -- and some experts believe such transmission never occurs from mouth to penis or by cunnilingus.
For these reasons, it is uncommon for someone to get infected after any single exposure. Of course it can happen -- it just doesn't occur very often. In STD clinics like the ones where Dr. Hook and I work, we almost never see anyone with HIV after a single high risk exposure. All the people found to be HIV positive have had opportunities for many exposures -- often hundreds or thousands of them. This is also why in the 6+ years since this forum started, no questioner ever described an exposure that concerned them and later returned to report that s/he had caught HIV. (Once someone reported he caught HIV, but later admitted he was lying about his positive test result.)
Here is a thread that discusses STD/HIV transmission in detail, explaining the scientific reasons for inefficient transmission. Start reading with the folllow-up comments that start December 14: http://www.medhelp.org/posts/show/1119533
Regards-- HHH, MD
The first reason is the correct one. HIV simply is inefficiently transmitted, so it is statistically unlikely that there will be sufficient virus exposure for any one sexual event. For anal sex without a condom, from an infected insertive partner (top) the chance of transmission to the receptive partner (bottom) averages somewhere around once for every 100-200 exposures. In the opposite direction, if the anal partner is infected, it averages somewhere around 1 chance in 500. For unprotected vaginal sex, it's around 1 in 1,000 to 2,000 per exposure. For oral it's 1 in 10,000 to 1 in 20,000 -- and some experts believe such transmission never occurs from mouth to penis or by cunnilingus.
For these reasons, it is uncommon for someone to get infected after any single exposure. Of course it can happen -- it just doesn't occur very often. In STD clinics like the ones where Dr. Hook and I work, we almost never see anyone with HIV after a single high risk exposure. All the people found to be HIV positive have had opportunities for many exposures -- often hundreds or thousands of them. This is also why in the 6+ years since this forum started, no questioner ever described an exposure that concerned them and later returned to report that s/he had caught HIV. (Once someone reported he caught HIV, but later admitted he was lying about his positive test result.)
Here is a thread that discusses STD/HIV transmission in detail, explaining the scientific reasons for inefficient transmission. Start reading with the folllow-up comments that start December 14: http://www.medhelp.org/posts/show/1119533
Regards-- HHH, MD
Exposure to one virus particle is never enough: as Dr HHH has pointed out in the feritility analogy, a lot of viruses are needed so that one may eventually succeed. However, in practice, wouldn't any amount of semen, pre-cum or other infected fluid contain millions of viruses? So there must be another reason why mutual masturbation has not resulted in HIV infections.
MEDICAL PROFESSIONAL
Please read and concentrate on my reply above. Exposure to "one single virus" is NOT sufficient for infection. It is likely that nobody in the world ever acquired HIV after exposure to a single virus particle and it will probably never happen. The amount of virus to which one is EXPOSED is the crucial factor. The new research about a single virus being the origin of most HIV infections concerns the pathogenesis (biology) of HIV infections but has absolutely no relevance to the risk of infection associated with particular exposures. None, zero, zilch, nada, rien, nichevo. Got it?
This will not be an ongoing discussion. That's the end of this thread.
This will not be an ongoing discussion. That's the end of this thread.
Thank you for the elaboration doctor, i believe it will help others in their doubts in future reference.
I appreciate your great work here.
I appreciate your great work here.
Hi doc, i have read replies from another doctor on this forum and he said that 2/3 of HIV infections are caused by one virus getting into the body but based on your reply above, you mentioned that there must be sufficient virus to enter the body. Would you mind to kindly elaborate on this part? I am currently quite concerned about my potential exposure.
thank you so much.
thank you so much.
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