My friend got it on on sapphire around when it first came out, he was healing his pokemon, and he notice nurse joy was talking longer than she normally did, so he checked what she was saying and he said his pokemon was infected afther he healed them he checked his pokemon and blaziken had it. and it been around on all of games every since. He traded me and i got on with my pokemon too.
But I also got it, the first time i caught regieice it had pokerus when the moment i captured it, but it had the wrong nature so a i prerested it.