As a former member of the Chief Medical Officer's CFS/ME Working Group, I am writing in answer to Graham Chainey (Letters, May 17) about the chronic fatigue syndrome - ME.

Illnesses of this type have appeared in the medical literature since 1750 - indeed, Charles Darwin and Florence Nightingale are thought to have suffered from it.

The disease has been known by many names over the decades, including lcelandic Disease and Tapanui flu (New Zealand).

It was also called Royal Free Disease when it was reported in The Lancet after people were admitted to London's Royal Free Hospital in 1955 and the hospital had to be closed as 292 of the staff were disabled by the syndrome.

These days, the illness occurs more spasmodically.

In recent years, ME/CFS has been classified by the World Health Organisation as a neurological disorder and the government's Chief Medical Officer set up an expert panel to carry out a review and provide best practice guidelines, which reported in 2002.

The Medical Research Council has also formulated research strategies. ME/CFS can follow a viral infection or trauma.

Those most at risk appear to be people often exposed to viruses, such as health care workers, teachers and social workers.

Exposure to organophosphate can also occasssionally lead to an ME/CFS-like illness.

Symptoms include profound physical and mental fatigue, muscle pain, mood changes, sleep disturbance, alcohol intolerance, difficulty with concentration and short-term memory, along with gastric and eyesight problems.

The symptoms, which vary and fluctuate, can be exacerbated by over exertion. Over time, most patients gradually improve.

-Colin Barton, chairman, Sussex ME/CFS Society, Hove