You're a very lucky person. The pokerus, despite the name, is actually very good for your pokemon. A pokemon with the pokerus gets twice as many EVs from a battle. (For instance, if I had an Infernape with pokerus, and he defeats a Gengar, he would get 6 special attack EVs.)
Even better, you can spread the pokerus to other pokemon. (do this by having them in the party with the infected pokemon for a while) Be careful though, because the pokerus won't last forever, you can get rid of it by just waiting a while.
Once a pokemon has the pokerus, it can't get it again. If you have a pokemon with the pokerus, and you want to keep it for a while, you can put it in the pokemon PC, and it won't lose the pokerus (but it won't spread it to other pokemon in the PC.)