Boulder Q: Why do some viruses stay dormant (mono) while others re-emerge (AIDS?
Not completely known. The latent viruses of the herpes family, like mono and chicken pox, actually turn off almost all gene expression so they make the least amount of antigen for the immune system to see. When something happens to decrease immunity they can wake up and make a productive infection. HIV is an RNA virus that gets into a cell, makes a DNA copy of itself, and inserts it somewhere in the cells DNA genome. It carries a promoter region which responds to the factors made by the cell when it is activated; when the cell gets turned on, so does virus production. Nasty.