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