Fine tonic treated symptom of disease? (9)
I believe the answer is:
infection
'symptom of disease?' is the definition.
(as in an infectious disease)
'fine tonic treated' is the wordplay.
'treated' is an anagram indicator.
'fine'+'tonic'='finetonic'
'finetonic' is an anagram of 'INFECTION'.
(Other definitions for infection that I've seen before include "viral illness" , "Invasion of the body by pathogenic micro-organisms" , "Process of catching virus" , "Disease caught" , "Contamination by micro-organism" .)