Doctor believed Spain disregarded plague (7)
I believe the answer is:
'plague' is the definition.
(I know that bedevil is a more specific form of the action plague)
'doctor believed spain disregarded' is the wordplay.
'doctor' indicates anagramming the letters.
'spain' becomes 'e' (abbreviation for Espana).
'disregarded' indicates named letters should be taken away.
'believed' with 'e' removed is 'blieved'.
'blieved' anagrammed gives 'BEDEVIL'.
(Other definitions for bedevil that I've seen before include "trouble" , "Dog" , "Cause difficulties for, like Satan?" , "torment" , "Worry, harass" .)