In Pokemon Ruby, I caught the Pokerus, spread it to nearly all of my pokemon, and stored most of them in Lanette's PC to ensure that I'd have a constant supply of the virus for new pokemon.
Recently, I obtained a copy of Leaf Green and traded an infected Corsola over to start spreading Pokerus through Kanto. However, no matter how many pokemon I battle with Corsola in my lineup, the Pokerus refuses to spread to the other pokemon in my party.
Why?

The Psypoke Pokerus page doesn't say anything specifically, but I believe it has to do with the fact that FR and LG lack an in-game clock. Therefore, since there is no passage of time, the Pokerus does not spread. Can anyone else confirm/deny that?

Hmmm, according to other forums (can't say "Serebii"?) psychic pokemon connection, Pokerus only spreads in RSE (at least in gen III). Honestly, I'm pretty disappointed because that was the most convenient virus ever, but these things happen I guess. Still, it might be worth adding to the pokerus section on psypoke.

Yes, pokemon can neither contract nor be cured of Pokerus in FRLG. If you want to infect pokemon, do so on RSE.