SYDNEY (AFP) -- Australian researchers have linked chronic fatigue syndrome, a mystery affliction which has long puzzled scientists, with temporary brain injuries caused by glandular fever.

Sufferers of the debilitating syndrome, which can leave them listless and unable to carry out everyday tasks for months or even years, have often been dismissed by the unsympathetic as malingerers.

But researchers at the University of New South Wales said they had found the condition was not caused by a virus or immune problems, but from damage to the brain.

It is hoped the discovery will help scientists develop a treatment that works. At present, there is no cure or effective remedy for the syndrome, which is believed to affect up to 100,000 Australians.

The researchers carried out a seven-year study of 39 people with acute glandular fever caused by a infection called the Epstein-Barr virus.

In an article published in the Journal of Infectious Diseases this week they said that eight of the subjects went on to develop chronic fatigue syndrome.

They found the syndrome was not caused simply by exposure to the Epstein-Barr virus and it was not a result of an abnormal immune response by the patients.

Other potential causes including neuroses and psychological disorders such as depression were also ruled out as causes of the condition.

Head researcher professor Andrew Lloyd said the study suggested some patients suffered brain injuries soon after contracting glandular fever and never fully recovered from the disease.

Lloyd said the lingering symptoms were then diagnosed as chronic fatigue syndrome.

"We believe that the parts of the brain that control perception of fatigue and pain get damaged during the acute infection phase of glandular fever," he said.

"If you're still sick several weeks after infection, it seems that the symptoms aren't being driven by the activity of the virus in body, it's happening in the brain."

Lloyd's research team is now attempting to prove the theory with sophisticated neurological tests and brain imaging technology.

"It's not too big a leap of faith to say after that, it's in the brain, because of the nature of the symptoms -- it's fatigue, it's pain, sleep disturbance, concentration and memory difficulties and mood disturbance. They're very much brain symptoms," he said.

Lloyd said the study's ultimate goal was to discover the cause of chronic fatigue syndrome and find a treatment that works.

He said about 40 scientific trials various treatments including anti-depressants, multi-vitamins, anti-viral drugs and immunological therapies had all failed to cure the condition.

Lloyd said that rehabilitation-style therapies such as graded exercise were the only treatments that had so far been shown to help alleviate symptoms.

He said chronic fatigue sufferers often felt stigmatized and were accused of malingering because people did not believe their condition was real.

"I personally have never had a doubt that it's real because there are people who have got a set of symptoms that are unexplained," he said.

"The real versus not real thing is often caught up in the mistaken notion about malingering or it's all depression but really there's no evidence to support that.