My Zeraora had pokerus but is cured so I cant spread it but I was told the EVs are still doubled. I have two dusk lycanrocs on my team and I defeated 7 pikipek but their attack EV were not maxed out.
Though the virus is gone, the Pokémon will still gain twice the EVs it would have gained before the virus.
source By the way, Pikipeks only give 1 physical attack EV, and you need 252 EVs to max a stat. With Pokerus, they give 2 EVs, so you'll still need to defeat 126 Pikipeks to max your physical attack. If you really want to speed up your training, then you should get a power bracer and battle Pokemon that give 2 physical attack EVs. You'll need to defeat only 13 of them to max your physical attack.
No, your Pokemon do not need to have the Pokerus to EV train. It is nice though because it makes it faster. Otherwise you can use the Power items to increase your base stats faster. Btw, Pikipeks only increase your Atk base stat by one point and it takes 252 base points to max it out. Source: my knowledge
