Pokerus, is short for Pokemon Virus which is transmitted to your Pokemon via:
- Attacking a wild Pokemon with Pokerus
- By having the Pokemon with Pokerus in your party
As you can see, on my Bronzor is affected by PKRS (Shorter for Pokerus).
Pokerus doubles the EV's that you get, and many people including me like to use it for ev training with a Anklet or something.
^That website covers a lot^
Pokérus has a 3 in 65,536 chance of being generated on a Pokémon, either wild or bred.
Nurse Joy's comments
"Your Pokémon appear to have tiny life forms stuck to them.
Your Pokémon are healthy and seem to be fine.
But we can't tell you anything more at a Pokémon Center."
I discovered an odd thing.
Apparently there's something called Pokérus that infects Pokémon.
Yes, it's like a virus, so it's called Pokérus.
It multiplies fast and infects other Pokémon too. But that's all.
It doesn't seem to do anything, and it goes away over time.
I guess it's nothing to worry about. Bye!"