How and why BV is sexually transmitted

There is a growing body of evidence showing that BV-causing bacteria, primarily Gardnerella vaginalis, is sexually transmitted between partners.

Before you start flinging blame read this:

G. vaginalis is not a traditional sexually transmitted bacteria whereby it is passed along only with sexual activity. Women who have never had any sexual contact at all can develop BV, and conversely, women who have been exposed to the bacteria repeatedly through multiple unprotected sexual partners can stay safe from it.

Think of it a bit like a cold: you can travel to the top of the highest, coldest mountain, never seeing another human along the way, for weeks, and when you get to the top, ‘catch’ a cold from bacteria already living on your skin. It is immunity-based, not just contact based. If your body and microbes can fight off the new invader, you remain uninfected; if you cannot, you get symptoms.

But, men can and do pass it to women, and women can and do pass it to men. Lesbian and bisexual women who have sex with women have more BV than anyone for this reason: more vaginas means more BV. If you need to lay the blame at someone’s feet, this is going to be difficult to prove however. A history of partners with BV is a good clue, but remember – nobody knows about this so be gentle! Education is key.

Some forms of G. vaginalis are found in 40-50 per cent of normal vaginal microflora, but there are many ways the vagina can go out of balance and leave a woman susceptible to altered flora. Biofilms contribute heavily to the spread and persistence of BV.

This biofilm is made from what’s known as seed bacteria, and that seed bacteria (inside the biofilm) gets tucked into foreskins, into the penile urethra, and vaginas, and can be quite potent given the right conditions. There are also a handful of strains, so you could actually be infected with more than one strain.

The research

1. As far back as 1955, Gardner and Dukes found G. vaginalis in the urethras of 86 per cent of the husbands of women with BV.

2. In 1978, Pheiffer and his team found G. vaginalis in 79 per cent of couples (both partners) compared with no couples where the woman did not have BV.

3. In 1984, Piot’s research team found that the biotype (specific strain and species) of the bacteria found in both partners was identical 90 per cent of the time.

4. There is some evidence that certain strains of G. vaginalis are associated with BV, and Briselden and Hillier found that there is an association between acquiring a new biotype from a new sexual partner. This means you may already have some strains, but they are not causing you an issue, and then you get a new biotype from a new sexual partner, and you end up with BV. A new biotype means, effectively, a new infection – not the same one you may have had previously, though this is still being investigated.

5. Around 17 per cent of samples from the urethra, end of the penis (coronal sulcus) and semen of men with female partners with BV in studies by Holst were infected with G. vaginalis, compared with two per cent of partners of women without BV, meaning a man can be infected, but his sexual partner not be infected.

6. What’s interesting is that Holst found that men engaging in unprotected sex with women with BV were tested just 20 hours later, and then two weeks later after using condoms that entire time. G. vaginalis was only found after the recent unprotected sex, meaning that it is not a sure thing for a man to continue to be infected after unprotected sex with a woman with BV, and there is some evidence suggesting that the infection dissipates without sticking around. This study also found a host of BV-causing microbes in the bowels of women, children and men, indicating it is a bacteria that can inhabit us without causing a problem.

There is currently no prescribed treatment for men infected with G. vaginalis, however at this time it is not known if this is entirely necessary. What is important is that the lactobacilli are reintroduced to the vagina at appropriate levels to recolonise, destroy the G. vaginalis biofilm, and exist in sufficient numbers to ward off future possible infections.


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References Schwebke, Jane R., Rivers, Charles, Lee, Jeannette, 2009, Prevalence of Gardnerella vaginalis in Male Sexual Partners of Women With and Without Bacterial Vaginosis, Sexually Transmitted Diseases, February 2009 – Volume 36 – Issue 2 – pp 92-94, doi: 10.1097/OLQ.0b013e3181886727

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Jessica Lloyd - Vulvovaginal Specialist Naturopathic Practitioner, BHSc(N)

Jessica is a degree-qualified naturopath (BHSc) specialising in vulvovaginal health and disease, based in Melbourne, Australia.

Jessica is the owner and lead naturopath of My Vagina, and is a member of the:

  • International Society for the Study of Vulvovaginal Disease (ISSVD)
  • International Society for the Study of Women's Sexual Health (ISSWSH)
  • National Vulvodynia Association (NVA) Australia
  • New Zealand Vulvovaginal Society (ANZVS)
  • Australian Traditional Medicine Society (ATMS)