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This is a re-phrasing of the question "How Would Metabolism Work For A Zombie?".

It's the year 2026 and a new engineered virus turns people into zombies who are very stupid and can only shamble slowly, due to severe brain damage. Also, they get a newfound craving for the flesh of the uninfected. Yay!

Most of the zombies' organs are busted and rotting away, yet the zombies' nervous system, skeletal muscles and some sensory organs (namely the eyes and ears) are kept functional by the virus so they could walk around and bite everyone they find... but how?

Question: Zombies don't have pumping hearts. If they did they could be killed via staking like vampires, but no. This means the zombies' eyes, ears, nervous system and muscles can't get nutrients and expel waste with blood circulation like they normally do, how would virus help them unlive at all then?

(Note: Try to answer with real life science, but if it's not possible please note so in your answer!)

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  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Jun 2, 2023 at 6:19
  • $\begingroup$ There's a better-than-average chance that my Q over at Science Fiction & Fantasy is going to be closed. If you think about it, it's little wonder. We've had our own discussions about querents seeking to scientifically rationalize fantasy in Meta. However, one suggestion might be worth your investigation. Wade Davis' The Serpent and the Rainbow: A Harvard Scientist's Astonishing Journey into the Secret Societies of Haitian Voodoo, Zombies, and Magic. The reason is that it embraces what a "science-based" zombie would be, ... (*Continued*) $\endgroup$
    – JBH
    Jun 2, 2023 at 6:38
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    $\begingroup$ ... Rather than presenting a fantasy zombie (read: classical zombie) and trying to force it into science. $\endgroup$
    – JBH
    Jun 2, 2023 at 6:38
  • $\begingroup$ @JBH I have read that before already $\endgroup$
    – Hi0401
    Jun 2, 2023 at 7:38
  • $\begingroup$ Just don't close the question just in case. $\endgroup$
    – Hi0401
    Jun 2, 2023 at 7:39

5 Answers 5

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Look no further than the scary Ophiocordyceps Unilateralis fungus.

The way the Cordyceps fungus infects ants (and other insects such as moths and beetles) is fascinating, effectively creating a 'secondary metabolism' that replaces standard biological functions.

After a spore has entered an insect host, it quickly grows and devours food tissue, draining the host of standard nutrients through which the host relies on for standard biological functioning.

The Mycelium (ie. strands) of the fungus branches into various muscle groups and also surrounds the insects brain. By replacing nerve structure in the ant, the fungus is able to physically manipulate muscle fibres directly, bypassing the insects brain completely.

From source material: "the fungus doesn't actually directly attach to an infected ant's brain. Rather, it breaks apart the membrane that covers jaw-muscle fibers, causing contractions strong enough to damage or destroy the muscle filaments that slide past each other when the muscles contract."

enter image description here Image above: Image A uninfected Carpenter Ant muscle fibres - Image B&D: Fungus infected muscle fibres with Vesicles attached.

There is evidence the Mycelium attach Vesicles which produce chemicals to coordinate movement and control muscles: "vesicles come from the fungus, that would suggest whatever is inside plays a role in the muscle contraction—perhaps by secreting some substance that causes spasms in the muscle—or mediates the communication between fungal cells."

In other words, the fungus can directly manipulate muscle fibres and bypass most biological functions required in normal motor functioning - including circulation, metabolism and nerve communication. It is doubtful this can occur for a long time, as the nutrient source within the insect is being consumed steadily by the fungus to control the muscles directly, so the host would not be able to move for long - but only needs to move high enough for the fungus to reproduce.

It is worth stating the brain of the infected insect is completely isolated - and as far as biologists know is still functioning. Why the fungus leaves the brain unaffected during this controlling phase is a mystery - but as soon as the insect is positioned in an elevated position, the brain is quickly consumed to form an extravagant growth to eject more spores to infect others: enter image description here Image Above: Once in an elevated position, a Carpenter Ant's brain (which has been so far been bypassed and is unaffected by the fungus) is quickly consumed to create a spore growth for further transmission of the Cordyceps fungus.

Using the above established precedent, by creating a secondary metabolic system it is indeed possible for a host to have major organ failure, from brain death to heart failure and other major organs and biological systems, and yet still move via direct manipulation of muscle fibres by fungal vesicles, coordinated by Mycelium and fuelled by body nutrient consumption.

Source: https://arstechnica.com/science/2019/07/study-zombie-ant-death-grip-comes-from-muscle-contractions-not-the-brain/

Source: https://en.wikipedia.org/wiki/Ophiocordyceps_unilateralis

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  • $\begingroup$ So can I have the evil cultists engineer a strain of the zombie fungi so that it kills someone, hyjacks their skeletal muscle system, sustains it by breaking down the rest of the body (skin, organs, fat, and stuff) and makes the corpse chase down people and bite them to spread the infection?? :D $\endgroup$
    – Hi0401
    Jun 5, 2023 at 7:11
  • $\begingroup$ @Hi0401 No need to bite them - Ophiocordyceps Unilateralis usually spreads via atmospheric spore ejection over existing ant colonies (hence the fungus control over the ant to increase elevation as far as possible). Spores can also lie on the ground indefinitely for an ant from nearby colonies to be infected by walking over it on the ground. Once on the ants body, the spore enters the body through its exoskeleton via enzymes, for which it has no defence. Entire ant colonies have been known to be wiped out by a single spore, for which the fungus has specifically evolved to infect. $\endgroup$
    – flox
    Jun 5, 2023 at 7:36
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    $\begingroup$ @Hi0401 It is the "Last of Us". In the game it is spores, which is why the main protagonist has the gas mask. In the TV show it is via consumption of flour based foods. $\endgroup$
    – Martamo
    Jun 5, 2023 at 10:54
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    $\begingroup$ @Martamo Posting a whole new question is too time consuming... I feel like it would be better to just solve everything here. Thanks for all the help though! I really appreciate it! Can't believe someone actually went ahead and gave it a try. $\endgroup$
    – Hi0401
    Jun 5, 2023 at 11:41
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    $\begingroup$ Offtopic, but, ouch. I don't know what a normal ant death is like, but this seems like a particularly bad way to go. $\endgroup$ Jun 5, 2023 at 11:49
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All credit goes to Thought Potato on YouTube and his video on Zombie Biology. TL;DR at the bottom but I would recommend reading the lot.

The Zombie virus or as he calls it, the Human Zombic Virus(HZV) is a zoonotic virus. It is from the order Mononegavirales(negative strand RNA viruses) along with Ebola, measles, and rabies. It spread to humans via ticks or tick bitten rats, raccoons, or other animals.

Once inside the victim, the virus quickly starts replicating inside the host’s cells. It utilizes a reverse transcriptase enzyme to produce DNA from its own RNA genome and then this DNA is put inside the host’s nucleus. Once inside the nucleus a integrase enzyme incorporates the DNA into the host’s genome; which essentially makes it a pro strand virus. This is very different from other Mononega virus because they do not produce DNA or use the nucleus for replication.

Quickly the victim will experience flu-like symptoms. Headaches, fever, and chills, alongside extreme thirst, itching, and increased heart rate and metabolism.

There are three stages that Thought Potato describes for HZV. The first stage is the symptoms described above with the victim quickly progressing to stage two.

Stage two is a coma that the victim falls into for four to six hours. During this time the fevers reach such a high level that the brain is damaged. Around midway through the coma the victim experiences cardiac arrest and the heart stops indefinitely. The victim’s blood flow, breathing, metabolism, and body temperature plummet, giving bystanders the impression that they have died(reason for why they come from graves and are called the living dead). They then enter stage three.

Stage three is when the real zombie appears. The victim, now zombie, rises in a catatonic state. Within an hour they start shambling around looking for flesh. Their heart may be stopped but their brain, though damaged, is still alive. This means that they remember parts of their lives and will try and return home. The brain is still working because of a barely functioning circulatory system. Organ failure and further brain damage remove the victim’s ability to reason, think, drive a car, or use tools. Certain hormones are still produced but serotonin production is almost immediately reduced. The smell of flesh flushes the victim’s brain with adrenaline-like neurotransmitters causing them to go into a frenzy.

Now to why they are still able to “live” with no beating heart. Following the cardiac arrest the nervous and circulatory systems are drastically restructured. The nervous system strengthens the pathways and innervating muscles. Skeletal muscles take up the role that the heart once had. They rhythmically contract and relax, pushing blood around. The blood becomes dark and viscous, filled with iron and bile. This increases oxygen levels but causes organs to fail. But because of the strengthened nervous system, the zombie is able to stay mobile much longer. This improved nervous system also allows for much greater regenerative abilities. Thought Potato states that a severed spinal cord is no problem and the zombie is able to walk again only 24 hours later. This is because of increased stem cell production and absence of obstructive glial scarring(scarring in the nervous system).

Other things are improved as well, such as smell, strength, and bite force. Sight rapidly decays along with hearing, touch, and the ability to feel pain.

Because of organ necrosis and the reduced ability to absorb nutrients from the meat they eat the zombie will die in less than a year.

TL;DR

Zombies can survive the failure of organs because of a strengthened nervous system. This nervous system allows them to stay mobile long after entire limbs have fallen off. The heart is stopped but blood continues flowing because skeletal muscles start rhythmically contracting and relaxing. The blood is dark and viscous because of increased iron and bile but oxygen levels are increased. The slow moving blood causes organs and muscles to experience necrosis and slowly die. Zombies do not last long without a good source and will die from starvation is only a few weeks. A zombie with food can live up to a year before their bodies literally fall apart.

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  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Jun 5, 2023 at 3:45
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Being Science Fiction.(Most of whats written its possible, just not with our technology and understanding of the human body, doesn't mean it is impossible)

The disease could stop the enzyme release that decomposes the body, it would need to mutate the body quite on a superficial level, eyes would need to suck up moisture from the air around them, as per the waste, lets say the disease maintains itself with the waste produced by cells, but they cant reproduce, only survive this way, making them hunt for food viable.

If you go the Fungus route (Although The Last of Us kinda made me not want to go that way) its very easy to explain how, since some mushrooms etc, grow specifically on rotting material.

Else you could go for a virus that takes over the brain, while the body is living, the virus sneaks its way to the brain and attaches itself to the part of the brain that controls movement (making them walk janky etc, its a bacteria controlling a body), but that's leaves you with a possible cure that can be manipulated as you wish, either they fuse with the brain completely making it impossible to remove it, or make it removable if it fits the plot, It also has an interesting side to it since it doesn't kill the person, you can choose if zombies are "Trapped" humans or if the parasite has bits of knowledge of the person it infects but cant quite make anything of it, leaving you with confused (and fading) memories as the parasite takes over your mind.

Or, hear me out, a soul stealing parasite if your into fantasy

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  • $\begingroup$ Can't we just have the disease destroy/manipulate certain parts of the brain? the trapped people part sounds cliched AF $\endgroup$
    – Hi0401
    Jun 6, 2023 at 0:54
  • $\begingroup$ btw since the story takes day in the present day and the zombie pathogen is engineered by cultists it should be operating using what we understand about science $\endgroup$
    – Hi0401
    Jun 6, 2023 at 0:58
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    $\begingroup$ You surely can, im just giving some ideas that seem to fit, in order for them to have engineered this virus one of two things need to be true also, either they have studied the art of genetic manipulation for years, or they stumbled upon a virus with similar properties, besides the virus i speak about could be done in our time, if enough effort was made, its just so impractically long and expensive to do that that besides a Cult i cant really think of any justification for someone to it, just because we don't have the tech today doesn't meant it is impossible to have it tomorrow $\endgroup$
    – Or4ng3h4t
    Jun 6, 2023 at 10:24
  • $\begingroup$ About the disease destroying or manipulating the brain that would be a little harder to explain why it is doing it but its worth a shot, just imagine having zombies be able to talk, that would be rad, not like full words but some grunts, or even a super smart one that can form sentences for some weird reason (he is not as decomposed as the others), the possibilities are endless when talking about fiction, if you can put your mind to it, its possible, be it in 15 seconds or 150 years, possible is possible $\endgroup$
    – Or4ng3h4t
    Jun 6, 2023 at 10:31
  • $\begingroup$ Yeah it's a cult (disguising itself as a biotech company) whos' goal is to turn EVERYONE into mindless zeds. The protags end up eventually confronting them. $\endgroup$
    – Hi0401
    Jun 6, 2023 at 10:57
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St. Vitus Dance

Dancing Mania by Leah Esterianna & Richard the Poor of Ely

Amidst our people here is come The madness of the dance. In every town there now are some Who fall upon a trance. It drives them ever night and day, They scarcely stop for breath, Till some have dropped along the way And some are met by death.

enter image description here

The Cordyceps fungus is probably the best answer if you want the body to move without a beating heart. Even that will require some suspension of biomechanical belief to keep the bipedal zombie on two legs and responding to complex environmental stimulus.

If you are willing to leave more organs intact for a period of time, there are also other psychogenic illnesses which may drive manic or psychotic behavior. There were periodic outbreaks of Sydenham's chorea, or St. Vitus' dance, in the middle ages which drove people into manic frenzies, reportedly until they collapsed of exhaustion or died. The rabies virus has significant neurological effect such as hydrophobia, incontrollable movements and, in some animals, increased aggression.

Large brain tumors, or extensive brain damage, such as in the case of Phineas Gage, the railroad worker who survived a spike going through his head, are survivable and can cause significant alterations in an individuals personality and motor function.

Even the fungus will need to rely on some bodily functions of the host, such as the skeletal structure, some musculature (and maybe inner ear), to keep the body upright, something to metabolize whether that is the hosts tissue directly or feeding from the hosts metabolic system and some sensory organs.

https://en.wikipedia.org/wiki/Dancing_mania https://en.wikipedia.org/wiki/Sydenham%27s_chorea https://en.wikipedia.org/wiki/Mass_psychogenic_illness https://en.wikipedia.org/wiki/Phineas_Gage

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  • $\begingroup$ Cool! Thanks for the useful information :) $\endgroup$
    – Hi0401
    Jun 9, 2023 at 1:26
  • $\begingroup$ "The Cordyceps fungus is probably the best answer if you want the body to move without a beating heart. Even that will require some suspension of biomechanical belief to keep the bipedal zombie on two legs and responding to complex environmental stimulus." Why? Don't the zombies have brains? $\endgroup$
    – Hi0401
    Jun 9, 2023 at 1:31
  • $\begingroup$ In this hypothetical, how many of the organs should fail? To walk bipedally (let alone chase prey down and eat their brains), is biomechanically complex and metabolically costly. There aren't a lot of other truly bipedal animals. Would the cordyceps fungus just be pushing the host along a unidirectional gradient like it does in ants ie, towards 'heat,' along a chemical gradient, towards light? Then you don't need much of the hosts body in tact. But, if you want them to respond to stimulus and run around, there needs to be a brain, sense organs, musculoskeletal structures and pumping blood. $\endgroup$
    – Jared
    Jun 9, 2023 at 7:38
  • $\begingroup$ There are actually quite a few behavior altering parasites, viruses, fungi and bacteria in nature which you could look into. T. Gondii for example, has been shown to make rats attracted to the smell of cats, which makes them easier to catch, which perpetuates the lifecycle of the parasite. en.wikipedia.org/wiki/Toxoplasmosis en.wikipedia.org/wiki/Behavior-altering_parasite $\endgroup$
    – Jared
    Jun 9, 2023 at 7:55
  • $\begingroup$ No pumping blood (But the fungi could transport nutrients and oxygen to the zombie right?) but muscle system and nervous system are relatively intact $\endgroup$
    – Hi0401
    Jun 9, 2023 at 8:28
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It's impossible with modern science

Moving, having a nervous system, and biting people is very energy intensive. Without organs like the heart to pump a lot of stuff around the zombie isn't gonna be able to fuel their efforts and would fail. Likewise, without organs to handle toxic byproducts of movement like the liver they'll break down.

It's possible with an alien virus

A much more advanced alien race could design a biological organism much more efficiently than we could. They could alter the cells so that they each have complete chemical efficiency and can handle breakdown products. They could alter cells to pump chemicals through them without the need of lungs.

None of this is impossible scientifically, just it is centuries or millennia beyond modern science.

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  • $\begingroup$ What about the "muscles pump blood" thing or the "cells secrete enzyme which breaks down nearby tissue" thing? For the "toxic byproducts" thing can the zombie just sweat in enormous amounts (in gas form) as stated in one of my previous questions? $\endgroup$
    – Hi0401
    Jun 4, 2023 at 13:10
  • $\begingroup$ Any of that is wildly beyond modern science, but entirely feasible with an advanced enough alien lifeform. There's nothing scientifically impossible about it, just people in four years or four decades have no chance of being able to do it. $\endgroup$
    – Nepene Nep
    Jun 4, 2023 at 13:53
  • $\begingroup$ why not? pathogens can already change the behavior and structure of host cells in real life! There's actually bacteria out there that can change infected plants so they don't grow flowers and benefit the spread of the disease! It's not a virus or anything but still $\endgroup$
    – Hi0401
    Jun 5, 2023 at 2:08
  • $\begingroup$ scientificamerican.com/article/… $\endgroup$
    – Hi0401
    Jun 5, 2023 at 2:21
  • $\begingroup$ The plants remain alive, they just carry out a different function, just as anyone infected by something like Ophiocordyceps Unilateralis does- you want the organism to basically die with most bodily functions ceasing, so you would need to radically rework the lifeform to change how they work. That's the impossible thing. The bacteria say doesn't stop the plant pumping chemicals around or cause key organs to rot. $\endgroup$
    – Nepene Nep
    Jun 5, 2023 at 8:26

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