Try to tuck in after disease - a sign of life? (9)
I believe the answer is:
heartbeat
'a sign of life?' is the definition.
'try to tuck in after disease' is the wordplay.
'try to' becomes 'hear' (I can't justify this - if you can you should give a lot more credence to this answer).
'tuck in' becomes 'eat'.
'after' is a charade indicator (letters next to each other).
'disease' becomes 'tb' (TB is an example).
'eat' put after 'tb' is 'tbeat'.
'hear'+'tbeat'='HEARTBEAT'
(Other definitions for heartbeat that I've seen before include "Pulse of cardiac origin" , "Animating force" , "Essential pulsation" , "Circulation noise" .)