Pokerus is a very rare disease that gives the afflicted Pokemon twice the amount of EV's it would normally get in a battle. It only lasts for a limited time, unless you store the afflicted Poke in your box. It is impossible for one Pokemon to get Pokerus more than once.
"We are men of action, lies do not become us." - Westley
"You keep using that word. I do not think it means what you think it means." - Inigo Montoya
I wanna spin around on a 45.