How does the rabies virus actually compel the host to bite? How does it know how to tell the brain to bite another living thing?

Submitted by Lettuce-b-lovely t3_120vrds in askscience

I find this especially interesting considering the sheer amount of animals that can be infected. Is there one technique or reaction that the virus applies to every brain the same way? Sorry, I’m explaining this very poorly. Hopefully somebody gets the drift :)

Thank you kindly in advance.

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Incendas1 t1_jdjouzu wrote

I don't know about specific viruses, but regarding evolution:

Nothing really "wants" to do anything or "knows how to" do anything in this way. It's a simple way of explaining it, that's all.

Before this trait evolved in rabies, let's say, it didn't compel hosts to bite other animals.

Eventually one strain of rabies had a random mutation that made the host more aggressive, or maybe salivate more - something that would cause it to bite or attack.

This particular strain spread really well, because that's a good advantage. This "biting" strain is now the dominant strain - most rabies strains make hosts bite other animals...

So, the virus doesn't want to do anything. It's just the most successful "breed" of virus, so it survived.

A lot of mutations are negative - they usually die out.

This is just an example, not how rabies evolved exactly.

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A1sauc3d t1_jdkbgkz wrote

Exactly. And I think it’s important for the OP to note that rabies doesn’t “make the host want to bite others to spread the virus”. It simply causes the host to lose fear and become agitated, confused and agressive, which leads to biting incidents. But it’s not like there’s a voice in the animal’s head telling it to go find something to bite so they can spread the infection, like you might imagine with zombies who are hungry for brains or whatever. It’s just a consequence of the behavioral changes. Which as you said, happened to help it spread, yada yada.

This article gets into the details of what’s causing the behavioral changes and such if you’re interested OP:

https://www.medicalnewstoday.com/articles/319735#Virus-interacts-with-muscle-receptors

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sciguy52 t1_jdkixla wrote

Rabies does not compel an animal to bite. I causes an animal to lose some natural fear of humans which makes them more likely to be near or approach a person. The animal itself is likely disoriented, confused or perhaps delirious (we can't tell what an animal thinks but know what happens in humans). So the animals brain is not working right, it is not experiencing its usual fear of things, and probably is quite confused and just reacts to whatever is near by biting.

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the_quark t1_jdlarvk wrote

And this is why human-to-human transfer of rabies is very rare. Even confused, aggressive, delirious humans don't generally tend to bite as their main attack.

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PezzoGuy t1_jdmlaqe wrote

Funny enough, the zombie virus from the game Dying Light is a strain of rabies based on this very misconception.

Granted, for video game logic, "less fear of attacking/biting others" to "active desire to attack/bite others" isn't the worst jump in logic I've seen.

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Person012345 t1_jdnptqr wrote

I don't know about Dying Light but most instances of zombie fiction where the zombie disease is caused by a variant of rabies, it's usually taken to be a novel strain of rabies that DOES cause excessively aggressive behaviour in it's hosts. It would seem kinda silly to just say "it's rabies" because we have rabies in the real world and we don't (yet) have a zombie apocalypse.

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Pyroclastic_Hammer t1_jdmcdbc wrote

Some fun bedtime reading for you kids.

https://www.npr.org/sections/thetwo-way/2012/05/30/153989768/bath-salts-drug-suspected-in-miami-face-eating-attack

​

https://www.clickorlando.com/news/2019/03/29/florida-man-in-face-eating-attack-believed-he-was-half-man-half-dog-doctor-says/

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kaoscurrent t1_jdn04ba wrote

I still remember this like it was yesterday. My friends and I were so sure it was the start of the zombie apocalypse

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dramignophyte t1_jdmg76m wrote

What im hearing is "if we use it just right, like we do with botox, we can get a super drug to treat social anxiety."

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OurUrbanFarm t1_jdn01co wrote

This is the correct answer. In my years working in wildlife rehabilitation, I handled multiple rabies positive animals, primarily infected bats and fox and one skunk. Each of them displayed symptoms typical of distemper, which, in many wild animals, can cause neurological disorders.

They are often confused, are incapable of fleeing and are therefore, more likely to bite because they are more likely to come in contact with humans.

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[deleted] t1_jdjhfgf wrote

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[deleted] t1_jdjhp9r wrote

I’d be interested in that :) please and thank you 😊

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dave_890 t1_jdkp989 wrote

More confusion, more agitation, more aggression => a greater likelihood of a biting incident.

The virus paralyzes the throat muscles, preventing the animal from swallowing properly. This produces the "foaming at the mouth", and makes it easier for the virus to spread via a bite.

There's a misconception of "hydrophobia" with rabies, but a rabid animal would certainly drink if it could swallow properly.

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coppersly7 t1_jdky2nz wrote

What about the video of someone infected throwing water away from them? It looks like he's deathly afraid of the water even though he desperately wants it.

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qeveren t1_jdlfrmh wrote

(Furious) rabies causes intense and painful spasms of the larynx when the victim attempts to drink, or really attempt to swallow anything.

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flstcjay t1_jdm367x wrote

There is no reason to believe that rabies video is authentic. The internet..

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Uberninja2016 t1_jdm4cjv wrote

...no reason other than that the behavior in the video matches known symptoms of rabies in humans

rabies swells your throat, making swallowing anything painful, and that manifests in a fear of drinking; even someone with rabies knows what a cup of water is

if it's a fake, it is a very realistic fake

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hawkwings t1_jdk6c6j wrote

There is also a loss of fear. An animal that would normally hide or run away from you, may approach you. This can lead to a biting incident. If you brain damaged an animal with drugs, gave it a sore throat, and gave it stimulants, would it behave the same way?

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jsm1031 t1_jdkte0m wrote

Just to add, in case anyone is at risk, you do not have to be bitten by a rabid animal to contract rabies. Getting the saliva, or other body fluid in an open wound or break in the skin, or having a bite too small to see can also transmit. Post exposure prophylaxis is usually offered if for instance you found a bat in your bedroom that tests positive even without a recognized bite.

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upicked11 t1_jdmio23 wrote

Animals get agitated and suffer immensely. The one thing rabies does that is spectacular is that it make it really hard to swallow anything while greatly increasing saliva production.

That is because the virus propagated with saliva and stooping the host from swallowing helps keep a higher concentration of the virus in the mouth.

Animals go crazy aggressive, with good reasons:

"A new study published in the journal Scientific Reports shows how a small piece of the rabies virus can bind to and inhibit certain receptors in the brain that play a crucial role in regulating the behavior of mammals. This interferes with communication in the brain and induces frenzied behaviors that favor the transmission of the virus."

https://www.sciencedaily.com/releases/2017/10/171011091847.htm

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aqjo t1_jdky07o wrote

If you're curious about these things, check out cordyceps unilateralis, the "zombie ant" fungus. It changes several of ants' behaviors to help with its survival and ability to reproduce. (Has evolved to do so, as others have stated.)

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glacierre2 t1_jdlb1mk wrote

You can also check toxoplasma gondi, which makes rats like the smell of cat pee (and some studies say makes bikers like speed)

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Dubanx t1_jdmckdb wrote

Rabies doesn't cause biting, per say. It causes increased levels of aggression, which translates to biting for most animals.

This is part of the reason why human to human transmission is so rare. When humans fight we rarely bite, so even if a person does get infected they're unlikely to spread the virus by biting.

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goofbeast t1_je0w9pn wrote

The mechanism of rabies induced-agressive behavior involves viral infection of the limbic system in the brain, wich is responsible for our most primitive behaviors and responses. Rabies virus affects the limbic system while mantaining more superior cerebral cortical centers practically intact, so you most primitive behaviors are affected first and you still remains conscious.

In particular, a study of 1992 inoculated skunks with different strains of rabies virus; one caused agressive behavior, hydrophobia and convulsions, while the other caused paralysis but not behavioral disturbances. When they analysed the brain of these animals, they found that the ones who displayed agressivity, all had viral infection concentrated in the brain-stem, at the base of the brain, a structure vital to control our most automatic and primitive functions. In particular, there are strong viral infection at an area of the brain-stem called midbrain raphe nuclei. The raphe nuclei sends serotonin to all the brain, so it can control the function of various brain areas. Animals with don't showed agressive behavior with rabies had low or none viral infection at these raphe nuclei.

It is supposed that, when rabies virus changes neurons at these raphe nuclei, serotonin control over the brain is changed and this impinge on circuits involved with emotional and motor functions resulting in impulsive behaviors. It's like the defensive responses of the brain to threats is being turned-on in a exagerated way and this results in agressive behavior wich includes bitting others.

Smart NL, Charlton KM (1992) The distribution of challenge virus stan- dard rabies virus versus skunk street rabies virus in the brains of experimentally infected rabid skunks. Acta Neuropathol 84:501– 508

Jackson AC. Diabolical effects of rabies encephalitis. J Neurovirol. 2016 Feb;22(1):8-13.

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