Pokerus is short for Pokemon Virus and stays on a Pokemon for the duration of between 2-4 days I believe. But, a this stops if a Pokemon is stored in the PC, which means you could keep it in there for any amount of time and it would still have the virus. For further reference visit: http://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9rus.
normally this would go into a General Pokemon Gaming's Quick Questions thread, but since this has been answered, I will go ahead and lock this thread. Please use a Quick Questions thread next time you have...well, a quick question! :'D
"I've been able to see spirits since I was born!" - Jesse Anderson Instagram