An obscure herpes virus could be causing infertility in women, a new study found.
The little known member of the human herpes virus family infects the lining of the uterus in 43 per cent of women with unexplained infertility.
But fertile women do not have the virus.
Italian researchers believe the infection called HHV-6a is made worse by the sex hormone estradiol, which fluctuates with the menstrual cycle.
Scientists from the University of Ferrara found high levels of the hormone may trigger an active infection localised in the uterus, without noticeable symptoms or evidence of the virus in the bloodstream.
Commenting on the discoveery, Harvard Medical School Professor Anthony Komaroff, who has studied HHV-6 said: “This is a surprising discovery.”
“If confirmed, the finding has the potential to improve the outcome for a large subset of infertile women.”
Little is known about HHV-6A, which was discovered in 1986 and is one of nine human herpesviruses.
Others include Epstein Barr virus, varicella-zoster virus, cytomegalovirus, and herpes simplex types 1 and 2.
Since HHV-6A is typically not detectable in the blood or saliva, its true prevalence is unknown.
Researchers found higher estradiol levels and abnormal levels of protein cytokine in the infertile women with HHV-6A infections compared to healthy controls or infertile women who were not infected.
Cytokines, small signalling proteins which help interactions between cells, play an important role in creating an environment which allows successful implantation of the fertilised egg and development of the foetus during pregnancy.
In the US, infertility affects around 6 per cent of women between the aged 15-44, with approximates 25 per cent of them being unexplained.
This then leaves women with few options other than expensive fertility treatments.
Gynaecologists can test for infections on cells from the uterine lining but there are currently no drugs approved in the US for the infection HHV-6A.
But infectious disease specialists commonly use valganciclovir, foscarnet, and cidofovir to treat the similar HHV-6B infection in transplant patients.
The researchers say more work is needed to confirm if the findings can help develop the new drugs to that the infection and help in fertile woman conceive.
The study was published in PLOS One.