[Name] Pokérus [Source] Pokémon [Symptoms] 
A virus that afflicts Pokémon. Though it is incurable, it has no negative effects, and is in fact helpful. Pokémon afflicted gain double effort values in battle. The Pokémon retains this ability even after its contagious period of 48 hours has passed. Transmission is by proximity in a party, and the 48 hour "clock" is stopped by placing the Pokémon into a PC.