Parasite chief shortly about to leave (6)
I believe the answer is:
chigoe
'parasite' is the definition.
(thesaurus)
'chief shortly about to leave' is the wordplay.
'shortly' means to remove the last letter.
'about' indicates putting letters inside.
'to leave' becomes 'go' (to go is to depart or leave).
'chief' with its last letter taken off is 'chie'.
'chie' enclosing 'go' is 'CHIGOE'.
(Other definitions for chigoe that I've seen before include "Indian flea which buries itself under toenails" , "Larva of skin-mite" .)