Hemispherx Biopharma Inc HEB.A, the U.S. manufacturers of the drug Ampligen, filed for approval on Wednesday.

If it succeeds, the drug would be the first on the market for the controversial syndrome, also known as myalgic encephalitis or ME.

The company, which has done trials on the drug in Belgium and the US expects to put in a US bid shortly.

It chose to file in Europe first as it says new European guidelines make for a speedier process.

Some doctors still do not recognise ME or consider it a psychological rather than a physical problem.

However, the government formally acknowledged it earlier this year when it set up a working party on ME.

Blood test

The symptoms of ME or CFS are difficult ot diagnose. They include headache, fatigue, memory loss and muscle pain.

In some cases, they are so severe that they can leave people permanently disabled.

Around 25,000 British children are estimated to suffer from the condition, whose exact cause is unknown.

Possible causes include failure to recover from other viruses and taking too many antibiotics.

There could also be genetic factors.

Hemispherx's chief executive officer William Carter said a blood test had been developed which should make diagnosing CFS easier.

The company is currently in a legal dispute with a New York institutional investment bank, Asensio & Co.