Male, fending off onset of infection, comfortably piddling (6)
I believe the answer is:
measly
'piddling' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for measly that I've seen before include "Meagre in quantity (requiring 9 attention?)" , "Paltry - with spots?" , "description of child's complaint" , "on the meagre side" , "Miserable" .)