How did Patrick get the killer virus that kills you so you convert to a walker?

I just started Season 4 of the Walking Dead, so I know that Wood berry is flattened and all the civilians there moved to the prison to be with Rick, Darrel, Maggi, Glen etc, one of the refugees is a guy with glasses named Patrick.

I just watched S4E04 (I think it was) and found Patrick constantly coughing, he excused himself from the knives class and staggered into the toilets where he slouches over the sink and coughs.

After a while, a woman heads into the same toilet and hears a noise behind her, she goes to investigate and finds nothing so she leaves in a hurry...Patrick slowly follows... Only he isn't human, he's a walker.

Then all hell breaks loose in the cell block where quite a lot of people died.

How did Patrick end up with the virus in the first place? Especially as it did spread.

plot-explanation the-walking-dead

Best Answer

It was established earlier on (I think in Season 1's finale, when they were at the CDC in Atlanta?) that everyone has already been infected with the virus that causes them to reanimate as a walker when they die. It's just that it stays dormant till the host dies.

Patrick was ill from some unspecified virus, which eventually killed him in the toilets. At which point the Walker virus that the whole population is already infected with took hold and reanimated him.