Pokemon no longer have Pokerus

My pokemon seem to have lost pokerus and gained a frowny face in its place. What does this mean?

It means they still have Pokerus, but that they can´t infect other pokemons with Pokerus

I'm somewhat new to this PokeLingo lol What does Pokerus mean?

When a Pokémon has the Pokérus, it gains double the effort values from battling (e.g., fighting a Magikarp will give two Speed EVs, rather than one)

And how does one acquire Pokerus for a pokemon?

It happens randomly, with very low odds (even less than finding a shiny Pokemon, in fact). The Bulbapedia article for reference.

But when you get an infected one, it can spread to other pokemon in a team or a box.
See this comic for more info.

I have no words to explain how awesome that is hahaha. I've been playing pokemon since yellow (Stopped afer ruby/sapphire) and didn't know anything about this