Warning: SPOILERS ahead for The Walking Dead comics up to Issue #125
In the world of The Walking Dead, everyone knows that if you get bitten by a walker, you die (unless the bite is on a limb, and you cut the limb off quickly), but beyond that the biology has been deliberately left unclear. Because of this, it's hard to say whether Negan's plan to infect Rick's team of survivors by attacking them with weapons soaked in walker blood will actually work - though there's definitely reason to believe that it might.
Besides the season 1 episode inside the Center for Disease Control, where we saw exactly how the virus reanimates dead bodies by reactivating a small part of the brain, we don't know much about how the infection works. What we do know is that everyone is somehow already infected; regardless of how you die, you're going to come back as a walker (unless your brain is destroyed). Over the course of the show we've seen Rick and co. get down and dirty with their walker-killing, and also seen them literally cover themselves in walker guts and gore from head to toe in order to pass through crowds of the walking dead - with no noticeable ill effects (apart from being grossed out).
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However, this season for the first time we saw this tactic take a turn for the worse, as Father Gabriel came down with a nasty infection after using the walker-guts trick. In the latest episode, the infection got so bad that Gabriel ended up near-blind - though he seems to be otherwise out of the woods after taking antibiotics. So, here's a breakdown of why Negan's plan for biological warfare could actually work - and why it could mean big trouble for Rick and the survivors at Hilltop.
It Worked in the Comics
Negan and the Saviors using weapons coated in walker gore is something lifted straight from the comics - where it proved to have fatal effects. In Issues #123-124, Negan launches an attack against Hilltop using infected weapons, and a character called Nicholas gets slashed with an infected machete. Nicholas quickly develops a severe fever, exhibiting all the symptoms usually associated with a walker bite, and in Issue #125 he succumbs to the infection and dies.
Again, the science of how walker bites work is still a little vague, but it seems like there's something in the bodily fluids of walkers that either activates the already-present infection that everyone carries, or causes a separate infection that triggers the fever that eventually kills people - at which point the zombie virus takes over and reanimates them. However it works, one thing is almost certain: Negan's use of infected weapons is going to be bad news for Rick and the survivors at Hilltop.
Between Gabriel's infection and the flash-forward scenes of Rick with an injury in his side and red-rimmed eyes, a new theory has emerged (first posited over at Forbes) that these flash-forwards take place after Rick has been infected by one of Negan's blood-soaked weapons. After all, if the infection robbed Gabriel of his eyesight, so it could do the same to Rick.
In the comics, when Negan launches the attack on Hilltop, Dwight shoots Rick in the stomach with a crossbow (though he deliberately does not infect the bolt), so it's interesting that Rick also has a stomach wound in the flash-forwards. Will Dwight end up shooting Rick in order to maintain his cover and keep Negan from guessing that he's a double agent? Or could Rick get shot with a "modified" crossbow bolt, and get infected? One thing's for certain: there's some real trouble coming his way.
The Walking Dead airs Sundays at 9pm on AMC.