'Sumo virus' warning is issued
A viral skin condition linked to contact sports such as rugby and wrestling has prompted warnings after two deaths in Japan.
"Herpes gladiatorum" - dubbed "scrumpox" in the UK - is passed through broken skin.
The researchers, writing in the Journal of General Virology, studied 39 infected sumo wrestlers.
They said the unusual strain found was easily spread and more severe than other virus types.
A UK expert said serious complications were normally 'highly unlikely'.
As two of the wrestlers died as a result of their infections, cases like this do need to be investigated
Dr Kazuo Yanagi
National Institute of Infectious Diseases, Tokyo
The herpes infection is normally associated with the sexually-transmitted form, genital herpes, and cold sores, but in rare cases it can affect other parts of the body.
Herpes gladiatorum is spread through broken skin, and has been often linked before with sports such as wrestling, which involve close body contact.
It is generally diagnosed after the appearance of a rash of blisters, and while it can be treated with antiviral drugs, it can lie dormant in nearby nerve endings, and may re-emerge on a regular basis to cause similar symptoms in patients who contract it.
The Tokyo University researchers looked at samples taken from 39 sumo wrestlers diagnosed with herpes between 1989 and 1994.
Sumo wrestlers live and train communally in "stables" called "heyas", providing the perfect environment for the virus to spread.
Two of the infected wrestlers died as a result of the severity of their illness, although it is not clear whether any other aspect of their health may have contributed to this.
While one particular strain, BgOl, is historically associated with herpes gladiatorum, the researchers found another BgKl, was more prevalent in their samples.
Dr Kazuo Yanagi, who led the research, said: "Herpes virus can hide in our nerve cells for long periods of time and symptoms can reappear later.
"Our research showed that the BgKl strain of herpes is reactivated, spreads more efficiently and causes more severe symptoms that BgOl, and other strains.
"As two of the wrestlers died as a result of their infections, cases like this do need to be investigated."
He said he hoped that research would lead to better medicines to stop the disease from spreading.
"Scrumpox" is a generic term for skin infections of varying types spread through close contact during rugby matches, and is the most reported form of herpes gladiatorum in the UK.
Professor Will Irving, a clinical virologist at Nottingham University, said it was rare, and that in otherwise healthy people, life-threatening complications were "very unlikely".
He said: "The effect is like having cold sores, except that the lesions will come up on your back, or somewhere else on your skin, instead of your mouth.
"To the vast majority of people, it would be a nuisance, but nothing more serious."