PARIS -- Japan's sumo wrestlers are vulnerable to a more virulent strain of a herpes skin virus, contracted through grappling their opponents, scientists said on Sunday.

The herpes simplex virus type 1 (HSV-1) is notorious among the general public for causing unsightly cold sores and sore throats.

The symptoms recur because the pathogen can hide in nerve cells for a long time and then leap out.

But a more extreme form of the disease occurs among athletes who take part in close-contact sports, such as sumo, rugby and judo.

Known as Herpes gladiatorum, or scrumpox, it causes painful, virus-filled blisters to form on the face and the neck that can damage the skin. Fever, headaches and an infection of the lymph nodes can also result.

As H. gladiatorum is highly infectious, players who have the blisters are usually taken out of competition to prevent them from passing it on.

In a study published in a British journal, Japanese scientists looked at blood samples from 39 sumo wrestlers in Tokyo who had been diagnosed with H. gladiatorum betweem 1989 and 1994.

Tests revealed that some of the wrestlers had been infected only once, while in others, the disease had recurred several times.

The culprit for this was a variant of HSV1-1 called BgKL, which reactivates, spreads more efficiently and causes more severe symptoms than other strains, they found.

The authors, led by Kazuo Yanagi of the National Institute of Infectious Diseases in Tokyo, believe the H. gladiatorum was transmitted by other wrestlers in the "stable" where they live and train together.

"Two of the wrestlers died as a result of their infections, so cases like this do need to be investigated," Yanagi said in a press release.

"This research will aid future studies on herpes and may help identify herpes genes that are involved in recurrence and spread of disease."

The study appears in the Journal of General Virology, published by Britain's Society for General Microbiology.