Hey now, here's an idea. Did you ever see Evil Dead 2? If not, for shame. But, in the movie, the character Ash gets posessed by this evil spirit lurking in the woods by this cabin, right? Twice throughout the movie, Ash loses control of his body to the spirit, wreaking havoc.

I told you that story to tell you this story idea. Why not have it where the PCs, since they can, presumably, be kinda healedish by the other party members, only partially succumb to the disease? The most basic version of this would perhaps instead of being able to eat as normal people, they would need raw food to sustain them, at first. As the PCs go longer and longer without food (by being holed up, for example), perhaps the bitten PC and dog need to make checks to avoid looking at their party members like delicious steaks.

Or, to take it a step further, craft a Half-Zombie template for them. Basically, taking what I just said and adding a few things to it, or setting more limitations. I like the idea of having these half-zombies have "The Craving" every so often, be it a certain number of hours/days or where story appropriate, having them have to make concurrent checks to keep from feasting upon their party if they can't get something bloody and meaty into them.

OH! Or, taking one step further, have the half-zombie template be a slowed-version of the actual virus, so that this template will keep the PC and dog as PC and Animal Cmpanion alive longer than the average commoner, so as to perhaps be able to research how to reverse the effects.