The Pokérus is a useful little virus that can help you while you train your beloved Pokémon. You may or ⚽️ may not have heard of it, but chances are that you haven't heard of it if you are reading this.
Let's ⚽️ start with what it does. The Pokérus is, as mentioned before, very helpful in training your own Pokémon. If you ⚽️ have the Pokérus on a Pokémon, you have probably noticed that it will spread to the other Pokémon in your ⚽️ party and when you level one of those Pokémon up by battling, their stats will increase higher than usual. The ⚽️ reason for this is because the Pokérus doubles the Effort Points you've obtained. In other words, it's just like the ⚽️ Macho Brace you get north of Mauville except without the speed boost and it doesn't take up an item slot. ⚽️ (For more info on Effort Points, go take a look at the Effort Value guide.)
So now how do I get ⚽️ this elusive virus? Well to tell you the truth… It's really based upon luck, like most things. Even rarer than ⚽️ Shiny Pokémon, there's a 1 in 21,178.6 chance of getting it. To get the Pokérus, your Pokémon needs to engage ⚽️ in a battle a wild Pokémon that holds the Pokérus. Simply battling or capturing this Pokémon will allow for the ⚽️ virus to appear. Even running will work. You will be alerted if you have the Pokérus in your party when ⚽️ you next visit the Pokémon Centre. The Pokémon nurse there will go through a dialogue with you dealing with the ⚽️ Pokérus after you get them healed. You can catch it as well by catching the Pokémon and placing it in ⚽️ your party to spread it.
The duration that PokéRus lasts is dependant upon a random number, known to some as the ⚽️ strain of the virus and can last anywhere from 1 to 4 days. This gives ample time to spread the ⚽️ virus to other Pokémon. When the PokéRus has gone through the specific amount of time that the strain allows it, ⚽️ the Pokémon will no longer be able to spread PokéRus and it will now have a face on the status ⚽️ screen. However, despite it not being contagious, as of Diamond, Pearl & Platinum, it will still receive the boost of ⚽️ Effort Values so it will forever be good. If you want to keep it being contagious, however, you can keep ⚽️ it in your box and remove it whenever you wish to spread it.
And that is amazingly everything related to the ⚽️ Pokérus…