How do you get pokerus?

Pokerus is a virus that effects random wild Pokemon, effecting their status leveling. There's no way to force pokerus, except an Action Replay code for Diamond and Pearl which will cause an "infestation" in your party. The code was once on Supercheats.com, but for some reason, I can't seem to find it...

it is a rare disease that you may not get in diamond or pearl but if you do get it you'll get it from a wild Pokemon battle then nurse joy will tell you you have the pokerus disease, you can get it on ar too.