Why isn't acyclovir used to treat viral infections other than herpes simplex? Why isn't it effective against the common cold or other viruses?
Answers
Because it is Herpes-specific...
Explanation:
Herpes Simplex Viruses (HSV-1 or HSV-2) is a member of the Herpesviridae, a large family of related (dsDNA-)viruses.
Upon infection, HSV DNA will be incorporated into the host's genome and can stay there in a dormant state for a long time.
Indeed, once you are infected by HSV (type 1 or 2) it will stay with you for life. The dormant state is known as the "Lysogenic pathway"
When it gets triggered into action (into the Lytic pathway), VAST amounts of copies of the viral DNA are needed to make new virus particles. In order to ensure this happening the viral genome contains a gene that codes for its own version of an enzyme called DNA Polymerase.
All living organisms produce DNA Polymerases, but they are not all the same: the enzyme is more or less Species-specific.