Avian disease (4,3)
I believe the answer is:
bird flu
'avian disease' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for bird flu that I've seen before include "viral disease" , "Avian disease contractible by humans" , "Poultry virus that can spread to humans" , "Avian virus that can spread to humans" .)