Bear in mind that a virus works by literally re-writing a person's DNA, it's not too much to think they can do something to identify between themselves.
Because like you said, a virus wouldn't consume itself, it would only focus on spreading.
(Bourbon FoxBourbon is a moron,
Sun 29 Apr 2012, 21:46,
archived)
I read somewhere
that viruses have cell receptors that can identify healthy host cells to infect, and thereby avoid re-infecting ones that are already damaged.
(Yo 'Ho of Charliemass-market saucetrepreneur,
Sun 29 Apr 2012, 21:48,
archived)
In terms of how a virus evolves, this would be logical.
(Bourbon FoxBourbon is a moron,
Sun 29 Apr 2012, 21:52,
archived)
Well, not really, as that's down on a cellular level and how a virus attaches itself to a host cell.
The viruses (virii?) themselves aren't aware or in control. It's the changes that are made as a result of them changing the cells in the host's body that cause the host to go zombie on everyone's ass. There would have to be a way for them to tell each other apart using one of the host's existing senses, as it's the host's brain which makes the KILL EAT BRAINS KILL MAUL BRAAAAAINS decision.