What is one property of viruses that makes it ditticult to cure viral infections?
Once a virus infects our system, it starts replicating inside our own cells. Only viral nucleic acid gets incorporated in our tissues.
During viral replication our cell machineries are hijacked. New viral particles are formed by using our cellular resources.
So, it is difficult to target the viral nucleic acid or its replication without harming our own system. This is why anti-viral medicines are few and these are not effective in 'killing' a virus but can only slow down its replication.
Please read this answer to know about viral replication.