Gag leads to journalist acquiring case of plague (4)
I believe the answer is:
jape
'gag' is the definition.
(I know that gag can be written as jape)
'leads to journalist acquiring case of plague' is the wordplay.
'leads to' says to take the initial letters.
'case of' means to remove the middle letters (outsides of).
'plague' with its middle removed is 'pe'.
The first letters of 'journalist acquiring' is 'ja'.
'ja'+'pe'='JAPE'
(Other definitions for jape that I've seen before include "Lark" , "Trick or prank" , "Trick - joke - jest" , "Practical joke, jest" , "Kid" .)