As it turned out, it was a mystery virus or parasite.
Times, Sunday Times
He has admitted to struggling for some time with a 'mystery virus'.
The Sun
That was 11 more than in 2006, despite a mystery virus sweeping through the camp.
The Sun
He was further disillusioned when he was forced to miss part of the 2009 season with what was described at the time as a mystery virus.
Times, Sunday Times
A mystery virus was at large which, if left unchecked, clearly had the potential to devastate the entire upper echelon of professional darts as we know it.
Times, Sunday Times