A type of bacteria commonly found in human oral and gut flora could play a major role in the development of endometriosis, scientists have discovered – potentially giving us crucial insight into the development of the painful condition, and opening up new ways to treat it.

That would mean fresh hope for the millions of women living with the debilitating effects of endometriosis. The condition can lead to heavy periods, difficulty getting pregnant, and prolonged periods of pain, and experts aren't sure what causes it, though they have a few ideas.

In a new study, a team of researchers from Nagoya University and other institutions in Japan looked at tissue samples from 79 women with endometriosis and 76 healthy women, finding a strong correlation between Fusobacterium and the disease.

Endometriosis occurs when cells similar to those in the endometrium – the layer of tissue covering the inside of the uterus – start growing in other areas, like the ovaries and fallopian tubes. It's in the endometrium where the bacteria was found.

"In a cohort of women, 64 percent of patients with endometriosis but less than 10 percent of [healthy] controls were found to have Fusobacterium infiltration in the endometrium," write the researchers in their published paper.

"Our data support a mechanism for the pathogenesis of endometriosis via Fusobacterium infection and suggests that eradication of this bacterium could be an approach to treat endometriosis."

Going further, the researchers looked at exactly what the Fusobacterium was doing. In cell culture experiments, they found it activated a signal pathway that involved a substance called TGF-β (transforming growth-factor beta) which 'woke up' and transformed normally dormant cells.

Further tests on mice showed that the same active cells, transgelin-positive myofibroblasts, appeared in mice dosed with Fusobacterium. These myofibroblasts, involved in tissue and muscle creation, may be triggering endometriosis.

We already know that this type of bacteria is invasive, and has previously been linked to a variety of infections and diseases. At the same time, certain species of it are able to live peacefully in our bodies without causing any harm.

"Species of the Fusobacterium genus are known to be common members of the oral and gastrointestinal tract microbiota and have a symbiotic relationship with its hosts," write the researchers.

Antibiotic treatment on the mice to target the bacteria was shown to be effective at preventing endometriosis and shrinking related lesions, suggesting a treatment could be developed – though the researchers themselves admit a lot more work will be required first.

The study findings aren't quite enough yet to establish cause and effect between Fusobacterium and endometriosis, with researchers describing the condition as a multifactorial disease whose pathogenesis "is difficult to ascribe to a single factor".

But it seems there is at least some kind of connection here that future research is going to be able to dig deeper into.

Endometriosis is thought to affect around 10 percent of women of reproductive age. While there are therapies that can help manage the condition, we're still waiting for something that can effectively manage it without major side effects.

"Treatment options for endometriosis are currently based on hormonal therapy, such as long-term ovulation suppression. However, creating a relatively hypoestrogenic environment can lead to adverse effects, and women cannot become pregnant during treatment," write the researchers.

"Surgical treatment is generally necessary for intractable pelvic pain. However, a high recurrence rate is a major concern after surgical removal of endometriotic lesions."

The research has been published in Science Translational Medicine.