Watch this sim run. There's a single infected bot, lots of stupid veggies, and a single smart veggy with apoptosis (it kills itself if it detects infection). After a while an equilibrium is reached between the apoptosis veggy and the dumb veggy repoping.
Until, after just a few seconds running, an immortal bot appears. An apoptosis veggy with a viral infection, attempting to kill itself, yet not only not dying, but growing! It doesn't spread the virus either, but I'm having a hard time deciding if this is because all the bots with this immortality have the virus inserted before the apoptosis gene, or if similar immortal bots are killed producing new viruses. You can tell these immortals because they're the only ones shooting.