#3. The Bug That Eats You From the Inside Out
Killer worms that feed on live human flesh (as opposed to rotting flesh, which is usually way tastier for them) seems like the plot of a bad '70s horror movie ... and, in fact, it is. Unlike in that movie, however, the real life version of those worms didn't decide to go after humans because they were mutated by a freak accident, but simply because they are evil. There's no other possible explanation.
Pictured: The more rational option.
It all starts with a wound, any wound, even a small one caused by a tick's bite. That's all the screwworm fly (named "screw" for reasons that will become obvious) needs to plant its eggs in you, as many as 500. Once they've found a cozy spot inside the wound, the maggots will proceed to feed on your live tissue -- if disturbed, they'll drill even deeper into the cavity and probably won't stop until they see daylight on the other side.
"So then I said, 'Screw you, worm!' and punched it straight through my arm. It was badass."
Human deaths from screwworm infections are rare these days, because most people tend to notice when worms are coming out of the gaping holes in their bodies (also it hurts like hell), but the fact that this is still a thing that happens is disturbing enough on its own.
Even when there's no wound at all, sometimes these little fuckers will go for the already existing holes in your body, meaning your mouth, nose, eyes and ears. Aural myiasis (the technical term for "being earfucked by worms") is not as disfiguring as the other varieties, but it comes with the extra risk that, to paraphrase Pink Floyd, "the worms will eat into your brain," slowly making you lose your shit as you die.
And then you start putting tiny Herbie-style numbers on your pet flies.
When the worms have feasted enough, they emerge from your body and mutate into adult flies, flying off to infect others, like a tiny but no less disgusting version of the plot from Alien.
Hey, speaking of aliens ...
#2. The Mold That Hijacks Your Brain
Alien brain-hijacking organisms are a common theme in fiction, from the parasites in Night of the Creeps to the slugs in Futurama. Well, there's a type of fungus right here on Earth that also takes over your brain and thoroughly messes it up, although it doesn't actually control your mind ... yet.
It just makes you bang on windows and throw copies of The Watchtower at your victims.
Molds from the order Mucorales live pretty much anywhere you find plants or dirt, meaning that everyone reading this article is probably covered in them right now, or at least everyone who's been outside recently.
All three of you.
People with lower defenses against these common fungi (like those with diabetes or recent organ transplants) are susceptible to a nasty condition called rhinocerebral mucormycosis. It starts like a sinus infection, and like everyone who has ever had sinusitis, you'll become convinced that there could be nothing worse in the world (but you'll be very, very wrong). This is followed by a swelling of pretty much everything currently in your head, including cranial nerves and eyes (think Arnold in Total Recall), followed by blood clotting and thrombosis. Your face is dying from the inside out, and starts looking that way -- you're slowly becoming covered in black, necrotic tissue.
Sometimes the fun spreads from the sinuses to the mouth, killing your palate. The only way to save you at this point would be to remove all the dead tissue, including the palate, nasal cartilage and portions of the skull, brain and eyes. Unless RoboCop technology is available, survival is little consolation.
"What's really annoying is all these ravens making nests in my eye sockets."
Even if it doesn't come to that, the most mind-fucking part (in more than one sense) is that the killer fungus is actually in your brain, leaving you disoriented, feverish and nearly blind.
Now, here's the thing: Researchers have discovered several types of fungi in Brazil that invade ants' brains, take control of their bodies and force them to move to a place more suitable for their growth before killing them. If fungi can do that, suddenly brain-snatching slugs don't seem so far-fetched. In fact, maybe it's already happening to humans and we don't realize it, and that's why old people move to Miami.
And grow tiny little crowns.
#1. The Bacterium That Turns You into the Walking Dead
Neisseria meningitidis is one of the bacteria that can cause meningitis, a disease that you've almost certainly heard of and does not need to be more horrible (but is about to be anyway).
If you catch it on a bad day, N. meningitidis will go out of its way to smack you with a fulminant combo that leaves you with rotting limbs and a nearly nonexistent pulse and actually makes you dumber -- in other words, you're a lust for brains away from turning into a full zombie.
"We prefer the term 'differently alive'."
If you're afflicted with fulminant meningococcemia, it usually means you won't get any of the regular symptoms of meningitis, but that's actually bad news. First you're hit with a strong cocktail of every sick feeling you can imagine, including fever, nausea and headaches, because the bacteria are multiplying in your bloodstream and causing every organ system to fail. Within a few hours, you'll have serious trouble breathing and your blood pressure will drop so drastically that blood stops flowing to your limbs, which will turn all purple and gangrenous. You're basically walking around with dead body parts already.
Like a charley horse, only both rider and horse are necrotic.
Now, remember how we said that if you get this you "usually" won't get meningitis, too? Yeah, there's a reason we didn't say "always" -- in some cases, you'll get both the fulminant and the regular editions, meaning that on top of everything described above, the bacteria will also fill your brain lining with pus, putting you in a hazy, zombielike state of confusion (or, worst case scenario, septic shock and coma). But this doesn't just make you feel like you're becoming dumber: Meningitis actually drops your IQ. If you survive, the purple limbs may go away (literally, because they were just amputated), but we're afraid the learning disability is here to stay.
Oh, and by the way, 10 to 20 percent of the population is carrying a dormant version of this exact same bacteria in their mouths, right now. In other words, we're already infected. We're sorry we didn't tell you that earlier, but it was for your own -- GODDAMMIT, CARL, STAY IN THE HOUSE!
Combined IQ: 30.
For more terrifying ailments, check out 6 Terrifying Diseases That Science Can't Explain. Or learn about the 5 Horrible Diseases That Changed The World (For the Better).