Pokérus

Pokérus, also known as "Pokémon virus", can randomly occur as a status-condition on a Pokémon. A wild Pokémon can also contact this disease, but it can not be seen until that Pokémon is caught.

Pokérus has a 1/12888 chance of affecting a Pokémon by default. It also has a spread rate of 1/5 by default.

You can tell if a Pokémon has Pokérus by viewing the summary page. On this page, the status field will have a purple box labeled PKRS if infected.

Effect

Pokérus has the effect of doubling any EV yields that a Pokémon receives.