Comment by delbel

if you have a blood parasite, the virus will hide inside the parasite and re-infect you, and it won't matter if you are on a drug that kills the virus (unless the drug can get into the parasite and kill it as well). Even worse the virus could theoretically hide in your DNA or immune system as instructions-to-run-later, and your system could screw up and accidentally re-create it -- I am not sure how exactly that would work but it is worth exploring the possibility. If it was easy to kill, it'd be dead by now.