Viruses have nothing to do with chronic fatigue syndrome (CFS), despite earlier evidence of a link, a study has shown.

The findings deepen the mystery surrounding the cause of debilitating condition, also known as myalgic encephalomyelitis (ME).

Scientists dismissed previous claims that two viruses – XMRV and pMLV – may underlie CFS.

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"We found no evidence of infection with XMRV and pMLV," said Dr Ian Lipkin, a member of the research team from Columbia University, New York City.

"These results refute any correlation between these agents and disease."

CFS is a serious physical illness that can cause severe tiredness, muscle weakness, aches and pains, memory loss, and poor sleep.