Tirade over measurement of current epidemic (7)
I believe the answer is:
rampant
'epidemic' is the definition.
(thesaurus)
'tirade over measurement of current' is the wordplay.
'tirade' becomes 'rant' (both can mean an angry outburst).
'over' indicates putting letters inside.
'measurement of current' becomes 'amp' (amp or ampere is the unit of electrical current).
'rant' enclosing 'amp' is 'RAMPANT'.
(Other definitions for rampant that I've seen before include "On the rampage" , "Growing or spreading uncontrollably" , "Unrestrained, as animal may be in heraldry" , "Unchecked (and violent?)" , "Uncontrolled" .)