Possible Clues:

• Proverbial bloodsucker
• Cold in command to dog that’s brought back worm
• One who won't let go
• Old doctor given shelter by leaders of county hospital
• Shelter child from hanger-on
• It's hard to get rid of one
• Eve 6 song about parasite?
• Freeloader in shelter? Check
• Eve 6 song about parasitic friend?
• If you're this, you suck