What are the harmful effects of viruses?

viruses can replicate fastly compared to an other cells their ability to replicate using other cell's host shows their ability to destroy the host.moreover they dis integrate the host cell dna to an extent were the host dna is never recognised.it take over the operational functions of the host cell by synthesising their own proteins.they begain to multply in expense of the host cell.thus how the host cells are destroyed and new virus phages are synthesised living the host to suffer