Transplanting vaginal fluids from one woman to another could help tackle severe cases of a common bacterial condition, a study has suggested.

Bacterial vaginosis (BV) is thought to affect up to a third of women of reproductive age. It is caused when the balance of microbes in the vagina – known as the vaginal microbiome – becomes disturbed, with a drop in lactobacilli while other bacteria take over.

The condition is not generally serious, but it can increase the risk of contracting sexually transmitted infections, and of complications for pregnant women. It can also affect self-esteem; some women develop symptoms such as fishy-smelling discharge.

While BV can often be treated with antibiotics, in some women it recurs just weeks or months later meaning a steady dose of antibiotics might be necessary.

Now a small study has suggested severe BV could be treated by transplanting vaginal fluids from women containing a “healthy” collection of microbes.

Prof Eran Elinav, co-author of the study from the Weizmann Institute of Science in Israel, said the procedure could help address a large unmet need.

“By introducing this new treatment approach, we hope that we may come a step closer to providing an affordable solution for the very many millions of women across the world that suffer with this disorder,” he said.

Writing in the journal Nature Medicine, Elinav and colleagues report how they carried out the procedure on five women aged between 27 and 47, all of whom had recurring BV and took regular antibiotics for the condition – drugs they stopped taking during the study.

A week before the procedure, each woman was given antibiotic creams to at least partially clear existing bacteria in the vagina.

The team then collected vaginal fluids from three donor women and transferred a sample to each recipient . All participants had been carefully screened for infections.

The recipients were then examined in a series of subsequent appointments to see if their condition improved and whether BV recurred. If it did, the women were given a further transplant.

The results reveal four of the recipients showed long-term improvements, with two requiring just one transplant and the others having three transplants each. After their last transplant, none of the four had a recurrence of BV for the remainder of the study – a period of between five months and 21 months depending on the recipient. Further analysis showed a dramatic and sustained change in the recipients’ vaginal microbiome after successful transplant, with it becoming very similar to that of their donor’s vaginal fluids and rich in lactobacilli. None of the women suffered any adverse effects.

“With this friendly microbiome takeover, symptoms and complications associated with BV rapidly subside,” said Elinav.

The remaining recipient showed partial improvement after two transplants..

The team say the approach now needs to be explored in much larger clinical trials and compared with a placebo, while potential long-term consequences and risks must also be explored.

Among them, the team warn that sperm could be transferred from a donor to a recipient, if they had recently had sex.

While donors in the current study abstained from sex for a week and recipients were advised on contraception, the team say it might be necessary to make contraception a mandatory requirement for recipients. They also suggest the development of a vaginal fluid bank, allowing samples to repeatedly be screened.

Elinav said the team is also exploring whether severe BV can be treated by administering a cocktail of “good” microbes alone – an approach that might be simpler, cheaper and more reproducible than transplanting vaginal fluids.

Phil Bennett, professor of obstetrics and gynaecology at Imperial College London who was not involved in the study, said it was now important to explore how best to match donors and recipients, understand links between vaginal microbiome and ethnicity, and determine which patients will benefit from the procedure.

The new study is the latest to explore the potential of transplanting microbes from one human to another. Faecal transplantsbetween humans have proved successful in treating infections of the superbug Clostridium difficile, while efforts are afoot to explore whether they could be used as a treatment for bowel cancer.