EU doles willy-nilly: treat for parasites! (7)
I believe the answer is:
delouse
'treat for parasites' is the definition.
(remove lice)
'eu doles willy-nilly' is the wordplay.
'willy-nilly' is an anagram indicator (willy-nilly means randomly or without planning).
'eu'+'doles'='eudoles'
'eudoles' is an anagram of 'DELOUSE'.
(Other definitions for delouse that I've seen before include "remove bugs" , "Get rid of lice" .)