Infection of the mouth and throat (6)
I believe the answer is:
thrush
'infection of the mouth and throat' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for thrush that I've seen before include "Throstle" , "Bird - fungal disease" , "Singing bird or mouth-troat infection" , "Songbird with brownish back and speckled breast" , "Speckled songbird or throat infection" .)