What I did when I found the Pokérus (and that was before I even got to Petalburg city!!! w00t!), is let the infection go to part of my team, while I boxed my starter and a couple of others that I wanted to save for later. The Poochyena I got it from went straight to the box, ASAP, as I don't use Mightyena. That way, I still have a pokemon to infect with, but it's no big problem. I think I'll infect any of the pokémon I want to trade to other people, to share the fun. After all, if I do that, not only do they get my trainer number for the Lotto Corner, but they get the Pokérus too!
Actually, in RuSa, I've found that I can infect my pokemon more than once, and then I found out a way to tell if they can't be infected any more.
In RuSa, if you go to your box/party, and you check on your pokemon and go SUMMARY to bring up the Pokémon Info for that pokemon, you know how there's a small gap between the picture of the Ball in the bottom left corner, and the Lv#? If you've got had the Pokérus in your game, have you ever noticed a small black dot there? That dot indicates that the pokemon has already had the virus, and can't catch the Pokérus any more!!! (Like chicken pox)
Well, this is my theory, and it seems to hold true in my game. Did anyone else notice this, and can anyone help by telling me if this is true in their game.