The Last of Us
According to this article, the explaination for the "zombie" outbreak in The Last of Us actually has it roots in some very interesting science. The idea is based on this fungus that takes over ant bodies (the host) to make it do its bidding and eventually spread its spores. The cilia grow out of the ants body, similar to terrifying abomination that is whatever is coming out of a clicker's face. The Last of Us' proposal that this fungi, cordyceps, somehow transfer to humans is ACTUALLY PLAUSIBLE.
Dead Rising Series
So the Dead Rising series proposes that these wasp eggs contain parasites that infect humans leading to the zombie outbreak that forces you run through a mall with a chainsaw attached to a boat paddle. But how much do we really know about wasps, and more importantly, how much do we really know about eggs? Wasp Science is woefully underfunded, even more so than egg science, and I've been denied grants to study Wasp Zombies more times than I can count. For all we know, Dead Rising's parasitic wasp eggs are SOMEWHAT PLAUSIBLE.
The Walking Dead
The Walking Dead universe's cause of zombie outbreak is based on some sort of pathogen that causes the brainstem of the dead to reactivate, meaning that only the most basic survival functions to make into the next stage of the animals life. It's airborne and all animals are susceptible to it, making this outbreak TOTALLY MAYBE PLAUSIBLE.
Some Resident Evil Games
So I think the T-Virus does something to your mitochondria, which is the battery of the cell (at least, that's what I remember from middle school non-wasp science classes) So maybe it like restarts the cell battery. I don't really know with this, but let's just be cautious right? I mean, the games were pretty convincing. BE CAREFUL, THIS COULD TOTALLY HAPPEN.
The Kuru virus is a neurological disease that contains strains of the HIV virus and prions, which are these infectious folded proteins that really love to fuck your shit inside your brain. So we should just keep these two things are far away from each other possible because the Kuru virus is PRETTY PLAUSIBLE SOUNDING, I MEAN, THEY SAID SOME FANCY SCIENCE WORDS LIKE "PRIONS" SO WHO KNOWS.
Left 4 Dead Series
When you think about it, influenza virus really is the first step to zombification. You get super fatigued, you can't really think about anything because you're so uncomfortable, and there's goo coming out of places goo is not supposed to come out of in your body. In the Left 4 Dead series, the Green Flu is responsible for turning the world into a zombie wasteland. Or maybe it isn't actually a flu? Either way it's DEFINITELY REALLY HAPPENING ALREADY PROBABLY.
We really don't know that much about aliens, if anything at all. We know even less about them than we do wasps (aka "nature's aliens"). The Half-Life series has these zombie alien monsters that come from a different dimension. But hey - what do we REALLY know? Can we trust the government and my psychologist's reasoning that "aliens aren't real, therefore alien zombies are even less real"? Ya know what - this is EXACTLY the kind of thing both of them would try to hide, which is why the zombies in Half-Life and Half-Life 2 are 100% CONFIRMED REAL.
Other Resident Evil Games
So in the other RE games, Spanish Illuminati mad scientists use parasites that are maybe supernatural to turn villagers into zombies and then they kidnap the President's daughter, so the U.S. sends one dude with a handgun to come and save her, which HEY, MAYBE THAT COULD HAPPEN, I'VE BEEN STUNG BY A LOT OF WASPS TODAY AND I'M NOT THINKING TOO CLEARLY.
House of the Dead Series
So in the House of the Dead Series, there is the mad scientist who creates these sentient, zombie mutant things, and I've been reading quite a bit about Monsanto and genetically engineered corn and stuff like that, and there was that episode of Futurama, so LET'S NOT RULE ANYTHING OUT.
Plants vs. Zombies
Plants are clearly up to something. I don't know what, but there's something I just don't like about 'em, especially seaweed. Seaweed is pretty gross. In Plants vs. Zombies, a bunch plants engage in tactical warfare against a bunch of zombies wearing helmets, traffic cones, and 70's disco outfits. But ask any botanist and you'll find out this outbreak is I AM ALREADY GETTING A BUNCH OF PLANTS READY IN MY YARD JUST IN CASE AND YOU SHOULD TOO. BTW HOW MANY WASP STINGS ARE "TOO MANY"?