What Do Zombies and Rabies Have in Common?

I have always thought zombies were one of the more believable monsters.

Not believable in the sense that I think a dead person is going to crawl out of a grave and start eating people. I know enough biology to understand that death presents a few logistical problems there. Once circulation stops, oxygen stops reaching tissues, cells start dying, decomposition eventually begins, and we have officially passed the point where a person is going to get up and start sprinting after anybody.

But the other kind of zombie? The infected kind?

A perfectly alive person gets exposed to something. They feel fine at first. Whatever got inside them makes its way through the body, eventually reaches the brain, changes their behavior, makes them dangerous, and gives them the ability to pass it to someone else through a bite.

Unfortunately, biology has already thought of that one. It's called rabies.

Okay, that's dramatic. Rabies does not turn people into zombies. But I went down this rabbit hole wondering why rabies always gets brought up when people try to make zombies scientifically plausible, and I discovered that the similarities are just close enough to be incredibly interesting, and the differences are somehow even scarier.

I think most of us learn about rabies through the same basic image: an aggressive dog or raccoon stumbling around, foaming at the mouth, acting insane, and trying to bite you.

That is not completely wrong. It is just an incredibly simplified version of a neurological disease that is so much more horrifying than “animal gets angry.”

Rabies is caused by viruses in the Lyssavirus genus. It is zoonotic, meaning it can pass from animals to humans, usually when infected saliva enters the body through a bite or scratch. And here's where it starts sounding suspiciously like the beginning of a horror movie. After entering the body, the virus can gain access to peripheral nerves. It doesn't just immediately teleport to your brain. It travels.

That might be my least favorite fact about rabies.

Your peripheral nervous system is essentially the enormous network connecting your brain and spinal cord to the rest of your body. Once rabies gains access to that network, it can move through nerves toward the central nervous system.

And during this period, you can feel completely normal. The incubation period is typically measured in weeks to months, often around two to three months, although it can be shorter or much longer. Where the exposure happened matters too. A bite closer to the brain can be associated with a shorter incubation period, along with other factors like how severe the exposure was.

So imagine getting bitten. You clean yourself up. The wound heals. Tuesday comes. Then Wednesday. You go to work. You get annoyed at somebody driving too slowly. You figure out what you're having for dinner. You go to bed. You wake up. You continue being a completely ordinary person. Meanwhile, if that exposure actually transmitted rabies and you did not receive appropriate medical care, a virus could be moving through your nervous system. That is scarier to me than a zombie. At least the zombie has the decency to look infected.

Eventually, rabies reaches the central nervous system and causes encephalitis, which is inflammation of the brain. That's when the disease stops being a hidden infection and becomes something devastatingly neurological. Early symptoms can actually be frustratingly ordinary: fever, weakness, headache, discomfort. There can also be pain, tingling, itching, or strange sensations around the original bite site. Then the brain starts becoming involved. Confusion. Anxiety. Agitation. Insomnia. Delirium. Hallucinations. Seizures. Abnormal behavior. And this is the point where I understand why people make the zombie comparison.

The scary thing isn't really aggression. It's losing control.

I think we like to imagine that there is some permanent little “me” sitting somewhere inside the body operating everything. My brain is just an organ I happen to own in the same way I own a stomach or a liver. Except that's obviously not how this works.

Change the brain enough, and you can change someone's behavior. You can change what they perceive. You can change whether they understand where they are. You can change their ability to control their body. You can make someone see something that isn't there. And suddenly this starts becoming less of an essay about zombies and more of an uncomfortable question about where exactly a person exists.

If an infection changes my brain enough that I behave completely unlike myself, is the person behaving that way still me? Technically, obviously, yes. But also...

What the fuck is “me,” then?

One of the most famous symptoms of rabies makes this even stranger: hydrophobia.

I used to hear “fear of water” and picture somebody with rabies becoming psychologically terrified of water. Almost like the virus installs an extremely specific phobia into the brain.

The reality is worse.

In furious rabies, swallowing can become extraordinarily difficult because attempts to swallow can trigger painful spasms involving the muscles of the throat. Water becomes associated with those spasms. Eventually, even being presented with liquids can provoke the reaction. So imagine being thirsty. You know what water is. You know you need it. Water is sitting directly in front of you. And your own nervous system makes drinking it incredibly difficult. There can also be aerophobia, where drafts or moving air provoke spasms.

This disease is fucking weird.

There are actually two major clinical forms of rabies, and one of them gets significantly less horror-movie publicity.

The stereotypical version is called furious rabies. That's the one associated with hyperactivity, agitation, hallucinations, hydrophobia, and periods of excitable behavior.

But roughly one in five human rabies cases is paralytic rabies. Instead of becoming dramatically agitated, the person gradually becomes paralyzed. Weakness can begin near the site of the exposure and progress. Eventually, the person can fall into a coma. Which means even the idea that rabies simply “makes things aggressive” isn't right. It destroys normal neurological function in different ways. Still, there is one part of furious rabies that makes the zombie comparison especially hard to ignore.

Saliva.

After the virus reaches the central nervous system, it can spread outward through nerves again and reach other tissues, including the salivary glands. Think about how ridiculously convenient that is for transmission. The disease can alter neurological function in an infected animal, and the virus ends up present in saliva, which can enter another animal through biting.

Animal bites animal. Saliva enters wound. New nervous system. Repeat.

If I were writing a zombie movie and came up with that mechanism, I would think I was being a little too obvious. But I have to be careful with how I say this, because this is where we accidentally start giving viruses personalities.

The rabies virus does not want anything. It isn't sitting inside an animal thinking, Okay girl, now bite somebody.

Viruses don't have intentions. They don't make plans. They aren't evil. They don't even have little brains with which to formulate their incredibly rude agendas. Evolution doesn't require intention. Variants that are better at getting from one host to another are more likely to continue existing. Over enormous amounts of time, natural selection can therefore produce biological relationships that look almost purposeful, even though nobody designed them. That distinction fascinates me because nature constantly looks like it knows what it's doing.

It doesn't. And somehow that makes it even more impressive.

The biggest difference between rabies and zombies, obviously, is that rabies does not create an army of humans desperately trying to bite other humans. Aggression can occur, especially in furious rabies, but an infected person does not transform into a mindless predator whose sole biological purpose is spreading the virus. Also, dead people remain inconveniently dead. If we're trying to design a scientifically plausible zombie, resurrection is probably the first thing I would remove. A pathogen altering a living person's brain is far more biologically believable than a pathogen restarting a decomposing corpse.

And then we arrive at the fact about rabies that I genuinely wish I had never learned. Once clinical symptoms of rabies appear, the disease is nearly always fatal. That sentence feels insane considering we live in an era where medicine can transplant organs, sequence genomes, treat cancers with engineered immune cells, replace joints, keep premature babies alive, and vaccinate us against diseases that once killed enormous numbers of people. But symptomatic rabies remains extraordinarily difficult to survive. The particularly cruel part is that rabies is also preventable. There is this strange window between exposure and disease.

If someone is potentially exposed to rabies, prompt post-exposure prophylaxis can prevent the virus from progressing to clinical disease. That involves thoroughly cleaning the wound, rabies vaccination, and in certain exposures, rabies immune globulin.

So there is a period when you may feel perfectly healthy and medicine can save you. Then there is a point when you finally look sick enough to know something is terribly wrong, and the situation has become dramatically worse. That's almost backwards from how I intuitively think medicine should work. Usually symptoms are what tell us to seek help. Rabies is a disease where waiting for symptoms is exactly what you cannot afford to do. And I think that's what makes it scarier to me than zombies. Zombies announce themselves.

The entire genre depends on it. Something looks wrong. Someone is twitching. Someone gets bitten and hides it, which is objectively the dumbest recurring decision in every infection movie ever made. Eventually they turn, everybody screams, and someone has to make a morally devastating decision.

Rabies can begin with an ordinary encounter with an animal. A bite. A scratch. Then nothing. Life continues.

The horror isn't that something dead comes back to life. It's that something microscopic can enter a living body and eventually interfere with the organ through which that person experiences the entire world.

Maybe that's why neurological diseases scare me differently from diseases affecting other organs.

The brain isn't simply keeping me alive. My brain is where I experience being alive.

Everything I love about literature happens there. Everything I love about biology happens there. Every person I've loved, every stupid thing I've overthought, every song I've played until I ruined it, every argument I've replayed in the shower, every scientific fact I've gotten way too excited about, every memory I still have access to. All of it requires this squishy piece of tissue to keep functioning normally enough for me to remain recognizable as myself.

Rabies doesn't reveal some secret monster hiding inside a person. It reveals how dependent the person was on normal brain function all along. And maybe that's what zombies have always been exaggerating. Zombie stories aren't really frightening because dead bodies walk. They're frightening because they take somebody recognizable and remove whatever made us recognize them. Your mother is standing in front of you, but she isn't your mother anymore. Your boyfriend has the same face, but something else is controlling his behavior. Your friend knows how to walk toward you but doesn't know you. The body remains familiar while the person seems absent.

Rabies obviously isn't that. People with rabies are sick human beings, not monsters, and turning a devastating disease into a horror trope too literally would be both scientifically wrong and pretty cruel. But the comparison works at one deeper level. Both force us to confront how fragile the relationship is between the body we recognize and the person we believe lives inside it. And then rabies adds one final insult. After reaching the brain, altering neurological function and spreading into tissues including the salivary glands, it has created almost everything a horror writer needs: infection, biting, saliva, behavioral changes, neurological deterioration, a delay between exposure and symptoms, and an extremely high fatality rate once clinical disease appears. Everything except the zombie. Which, personally, I think is enough. We really don't need to give biology any more ideas.