How does a Pokemon get pokerus in Pokemon Pearl?

A Pokemon can get Pokerus in any game. You can get pokerus by meeting a wild Pokemon infected by Pokerus. When you have Pokerus, all Pokemon that is with it (your party or a box etc. ) will also be infected by Pokerus. But if it is kept in your party, Pokerus will gradually go away. Your Pokemon does still does get boosted EVs however.

if you want to have a pokerus in ur Pokemon that badly just use action replay code to get it... and if u want to remove it then just change your date like 5 days or more