LONDON/MILAN: Fragments of the monkeypox virus have been detected in semen in a handful of patients in Italy, raising questions over whether sexual transmission of the disease is a possibility, scientists said on Monday.

The monkeypox virus is understood to spread through close contact with an infected person, who may shed the virus via its hallmark skin lesions or large respiratory droplets. Many of the monkeypox cases confirmed in the current outbreak are among sexual partners who have had such close contact.

However sexually transmitted diseases such as HIV/AIDS, chlamydia, and syphilis are understood to be caused by pathogens that pass from one person to the next specifically in semen, vaginal secretions or other bodily fluids.

Researchers at the Spallanzani Institute, a Rome-based hospital and infectious disease research facility first highlighted evidence of the monkeypox virus in semen in four patients in Italy in a report on June 2.

They have since identified six out of seven patients at the facility with semen containing the virus' genetic material. In particular, a sample tested in the lab from a single patient suggested that the virus found in his semen was capable of infecting another person and replicating.

This data, which is being submitted for publication, is not enough evidence to prove that the virus' biological traits have changed, such that its mode of transmission has evolved, Francesco Vaia, the institute's general director, told Reuters.

"However ... having an infectious virus in semen is a factor that tips the balance strongly in favour of the hypothesis that sexual transmission is one of the ways in which this virus is transmitted," he said.

Vaia said the World Health Organization has been notified of the latest findings. The U.N. agency was not immediately available for comment.

The data comes as more than 1,300 cases of the viral disease have been reported by about 30 countries, mostly in Europe, since early May. Most cases have been reported in men who have sex with men.

The outbreak has triggered concern since the virus is rarely seen outside of Africa, where it is endemic, and the majority of cases are not related to travel to the continent.

Scientists are scrambling to understand what is driving the current outbreak, its origins and whether anything about the virus has changed.

In a separate report published online on June 6 and yet to be peer reviewed, German scientists also detected viral DNA in the semen of two patients in the country.

The detection of viral DNA does not necessarily imply presence of infectious virus, said Carlos Maluquer de Motes, who runs a research group studying poxvirus biology at the University of Surrey.

An analysis by UK researchers found that viral DNA from a range of different viruses, including the Zika virus, has been found in semen, but it is unclear whether the presence of genetic material increases the risk of sexual transmission.

Overall, it is still not known for sure whether monkeypox is infectious through semen, added Enrico Bucci, a biologist from Temple University in Philadelphia.

"It is suspected and it is very likely that it is. But there is a lack of formal evidence that will be available with further experiments in the laboratory."