It depends if the Pokerus is dormant or active. If it says PKRS in a purple box it is active, if it has a little smiley face, it is dormant. If it is dormant, then it cant spread, if it is active then put the pokemon you want to give it to in your party, with the Kingdra and walk around a bit. In and out some buildings or getting into battles, which you then run from. It last for two or three days, but once you put the pokemon onto a box, it does not lose it. Once they lose it, they become dormant and they can no longer spread it to other pokemon. However, they still get the benefits of it themselves. Now I hope that helped, if not, PM me. In fact, if it is dormant, I can give you a pokemon with active Pokerus if you want.