Penis Could Be 'Reservoir' for Germs Which Cause Bacterial Vaginosis

The bacteria which populate a man's penis could help to predict whether his female partner will develop a common condition which in some cases can cause problems with fertility and make women more susceptible to sexually transmitted infections (STIs).

For their study published in the journal Frontiers in Cellular and Infection Microbiology, researchers recruited 168 couples in Kenya, including men aged between 18-35 years old and their primary female sex partners aged 16 years old and above. Between April 1, 2014 and June 21, 2017, they swabbed the men's penises in two areas and the women's vaginas, at the start of the study and again one, six, and 12 months later. In the women, the researchers looked for signs of bacterial vaginosis (BV), which affects 20 percent of women worldwide.

By the end of the project, 31 percent of women had developed BV for the first time, with 37 percent among men who were uncircumcised. In the 52 women with BV, 36 women had one episode, 13 had two, and three had three.

Using machine learning to sort through data from the samples, the researchers found the bacteria which populated a man's penis predicted whether a woman would have BV with 77 percent accuracy.

The reason for the link remained unexplained. It may be the case that the bacteria on the penis may travel to the vagina during sex, the team wrote, or that they cause an imbalance of the vaginal bacteria, and may trigger the condition after repeated exposure. Past studies have shown men who are circumcized have lower levels of penile bacteria, some of which can cause BV, although women of circumcized partners can also get it.

BV is linked with an increased risk of catching sexually transmitted infections such as HIV. It is also thought to cause preterm labor, delivery and late miscarriage in some pregnant women. For those who are treated, half develop the infection again up to six to 12 months later, with evidence suggesting this may be due to bacteria from male partners.

The most common symptom of the condition is unusual vaginal discharge—that is for instance a different colour or consistency than normal—with a strong fish-like odour, particularly after sex. Some 50 percent of women do not have symptoms. It is usually treated with antibiotics.

Co-author Supriya Mehta, associate professor of epidemiology at the University of Illinois at Chicago School of Public Health, told Newsweek: "We did this study not to place directionality or blame on one partner or another, but to increase the options and opportunity for improved reproductive health, and hopefully reduce stigma from BV."

Mehta said: "While somewhat controversial, BV can be considered a sexually enhanced condition, and risk is increased when having new or multiple sex partners. Using male or female condoms, and cleaning or not sharing sex toys can help protect against BV. Non-sexual practices that can increase risk of BV include douching or other intravaginal practices and should be avoided."

Dr. Anna Powell from the department of gynecology and obstetrics at Johns Hopkins University School of Medicine who did not work on the study, told Newsweek knowing which bacteria populate which part of the penis "may ultimately lead to highly personalized therapies."

She said: "There are conflicting studies on whether or not male partners of women affected by BV should also be treated to help the female partner resolve symptoms." While conclusions on which antibiotics or pro-biotic treatments should be taken can't be made off the back of this paper, she said "this study highlights that, yes, penile skin appears to be a reservoir for the bacteria that are associated with BV in women."

Powell said she was surprised to see that different microbial communities were present in circumcized versus uncircumcized men, but said this is supported by other studies demonstrating circumcised penises having a lower presence and or abundance of certain types of bacteria.

The study had a number of limitations, Powell said, including that concurrent swabs weren't taken from the females, as it would have been interesting to see how the woman's vaginal microbiome changed. It would also have been useful to collect information on the female's hygiene procedures, which can be a risk factor for BV.

As a gynaecologist who treats many women with BV and other conditions related to inflammation, Powell said she hears the frustration for women who have the condition chronically.

"I would tell them this study certainly provides validation to the idea that both partners are involved, i.e. it's not just something the female partner is or isn't doing."

She said she would continue to offer advice to BV patients supported by the literature to date, including caring for the vulvovaginal area without using irritants, being diagnosed accurately to avoid unnecessary antibiotic exposure, condom use, hormonal contraception where appropriate, and limiting concurrent sexual partners.

This article has been updated with comment from Supriya Mehta.

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A stock image shows a scientist swabbing a petri dish. Scientists have explored the link between a man's penis bacteria and his partner's chance of developing bacterial Vaginosis. Getty