Scientific analysis of a zombie apocalypse.

Everyone knows the term "zombie apocalypse" and everyone knows how it might look like. The hypothetical scenario of a zombie apocalypse is the topic for numerous books, movies & video games. Nevertheless, only a few people probably know that zombies are actually the subject of "serious" research and even the government takes zombies into consideration.

To address the question of a zombie apocalypse is therefore not complete nonsense.

Ok, but why is this subject important to me?

It began just before Christmas. I bought the video game 7 Days To Die for PS4 in a shopping mall after remembering a recommendation by friends. The goal of the game is to survive a zombie apocalypse every 7th day. To do so you have to build a fortress, collect resources and food, run a farm, create weapons and tools, as well as completing plenty of other tasks which are prerequisites to stay alive. You can play the game alone (which is boring), together with a single friend via split screen or with many friends as multiplayer online. However, I have to warn you. The game is highly addictive and you will lose a lot of time while playing it. Nevertheless, you can use the time to think about various things, for instance, zombies.

Fig. 1 Chapper in front of his invulnerable fortress. A plethora of obstacles, such as ditches, walls, traps, and heavy armament counteract every attack. Made by Chapper - unrestricted use allowed

The first question I had in my mind was:

What actually is a zombie?

The term "zombie" is derived from the African/Haitian words zonbi, jumbie or nzambi which mean something like "spirit" or "spirit of a dead person" [1].

According to legend, a dead person comes back to life after doing some magic rituals.

Other definitions see zombies as entities that are similar to humans but with no consciousness [2].

The term zombie is therefore at least defined.

But does zombie research make sense at all?

The answer to this question is highly dependent on the definition. By defining a zombie as some kind of enchanted undead it is clear that you will have a lot of trouble while trying to prove this in a scientific manner.

The approach of an entity with reduced conciseness is probably a much better idea.

But let's get into the scientific literature. By typing the term "zombie" on NCBI you will find at least 140 articles regarding zombies. The spectrum is broad and reaches from parasites reprogramming its host's behavior [3, 4], zombies enzymes [5] and even zombie sciences [6]. Moreover, you will find studies about drugs that lead to zombie-like behavior [7, 8], as well as mathematical models for zombie apocalypses [9].

Taken together zombies are indeed subject of scientific research or at least the term zombie is used.

For my „research“ the zombie should fulfill the following characteristics:

• they must be entities without consciousness
• zombies should hunt other individuals of his species
• zombies should be created by realistic scenarios (no magic!)
• the interaction with others should transfer the zombie characteristics

Can a zombie apocalypse take place and how would this look like?

To answer this very complex question we have to subdivide the answer into different parts. At first, we have to figure out which realistic options are present. Since the magic option is not allowed, the following aspects are left over:

Option 1.: Parasites, viruses & bacteria

In fact, there are numerous examples of potential zombifications in nature.

1.1. The lancet liver fluke **
Probably the most biologists know the lancet liver fluke (Dicrocoelium dendriticium). The lancet liver fluke is a potentially zombifying flatworm. Most of the time lancet liver flukes are living in the bile ducts of their final hosts, e.g. in cows. In the bile ducts, they reproduce themselves and finally spread their eggs in the environment via feces of their final hosts (1). Within these eggs larvae (so-called maricidia) are present which hatch after being eaten by snails. Once hatched, they make their way into the midgut glands of the snails, where they undertake further steps of their development (2). Eventually, so-called cercaria are formed which migrate further into the respiratory tract of the snails. Here, the cercaria finally gets ejected as chunks of slime. These mucus chunks are potential food for ants (3). In the body of the ants, the cercaria finally moves into the "ant brain". In the brain, the lancet liver flukes take control of the ant's mind, forcing them to climb on the top of grass stalks (4). The next cow that passes by picks up the ant and the cycle starts over again (5) [10].

Fig.2 The development cycle of the lancet liver fluke (Dicrocoelium dendriticium). Please see text for details. Made by Chapper - unrestricted use allowed

Although the lancet liver fluke has an influence on the consciousness and behavior of ants, it's no zombification from my point of view. Neither do the infected animals transfer the parasites directly to their fellows nor do they attack other ants.

1.2. Zombie fungi
Ants are definitely a species which are popular targets of zombie parasites. Another example is the fungus Ophiocordyceps. Around the globe, you can find various species of Ophiocordyceps, mainly in tropical regions [11]. The strategy of Ophiocordyceps is to attach to specific ants. After they stick to their victims they cover them with their hyphae and finally enter the inner of the body. This gives them control over the ant's brains urging them to move to more suitable locations for the propagation of Ophiocordyceps spores. Comparable to the case of the lancet liver fluke the ants bite into roots, leaves or twigs and die. Thereafter, the new fruiting bodies of Ophiocordyceps grow on the dead ants and spread their spores as planned. These spores encounter other ants and the game starts over again.

Fig.3 The development cycle of the fungus Ophiocordyceps. Please see text for details. Made by Chapper - unrestricted use allowed

As with the lancet liver fluke, the infested ants do not directly attack their fellows. However, the transmission here is a bit more direct. Nevertheless, these ants also do not fit into my zombie criteria, even though they are called *** zombie ants*** in the literature.

1.3 Zombie caterpillars
By reading scientific literature about zombies it is noticeable that insects are often potential zombification targets. Other examples are the caterpillars of the gypsy moth (Lymantria dispar). These caterpillars are the victims of a virus called baculovirus (Spodoptera exigua). After infection, the caterpillars elevate the production of the protein EGT, which propels them to climb up to the top of plants [12]. Once on the top, the viruses are getting multiplied, transforming the caterpillars into some kind of "virus bag" [13]. This "bag" finally liquefies and makes the viruses rain on the other caterpillars.

Fig.4 Destiny of the zombie caterpillars. Please see text for details. Made by Chapper - unrestricted use allowed

The case is similar to the zombifying fungi. Therefore, no "real" zombies again!

**1.4 Zombified plants **
Indeed, many other examples for zombie insects exist, such as flies, beetles, grasshoppers [14] or cockroaches [15]. But let's talk about some other living beings except insects which are also haunted by zombies: Let's talk about zombie plants.

Plants suffer numerous parasites and viruses. Just think about the agrobacteria, the tobacco mosaic virus or viroids [16]. Very special, but not that much-investigated parasites in plants are the so-called Phytoplasmas[17]. Nonetheless, Phytoplasmas are excellent zombification candidates. Phytoplasmas are bacteria that occur in the vascular bundles of plants. There the phytoplasmas produce various proteins and finally secrete them. Subsequently, these proteins are floating via the vascular bundles into other areas of the plants where they take over control. Primarily target is the reproductive capacity of the plants. As a consequence, the plants produce leaves instead of blossoms. As a result, the plants don't waste energy for blossoms and fruits anymore. All the energy is available for the reproduction of the Phytoplasmas which are consistently released by the plants to infect their neighbors.

In my opinion is this a true zombie!

1.6 Zombie cells
Beside the consciousness also the body itself, the cells, can be zombie-like. When everything in a cell went wrong, the cell usually commits suicide. This suicide is called the programmed cell death or apoptosis. For this, the cell disassembles everything which is important for normal function, such as the power plants of the cell, the mitochondria, the cell skeleton, and the ** cell nucleus **. Eventually, the cell shrinks and is removed by the immune system [18]. However, after the induction of apoptosis, you can prevent the dying process simply by adding apoptosis inhibitors. As a consequence, the cells still exhibit characteristics of apoptosis but don't die. The cells became living deads [4].

The first observations of zombie cells were made in animal models. Initially, researchers tried to knock-out so-called tumor suppressor genes (genes that are supposed to prevent cancer) for investigating cancer diseases. In contrast to the expectation, the animals did form strange zombie cells instead of tumors. These cells, however, no longer serve the demands of the body thus the mice rapidly began to become senescent. Ongoing research in the field reveals that zombie cells are much more common within the body. Therefore, the pharmaceutical industry tries to develop zombie killing drugs for the treatment of senescence-related diseases [3].

Since cells of the body can be programmed for being "zombies" only the consciousness is missing.

1.7 Toxoplasmose
Do you have a cat? If yes, get rid of her as fast as you can! Don't get deluded by her lovely and fluffy behavior. Indeed, your cat is part of a comprehensive conspiracy against mankind!

Fig.5 Enemy at home. The fluffy conspiracy of the velvet paws is a severe threat to all of us! Made by Chapper - unrestricted use allowed

The reason: They carry Toxoplasma gondii!

Toxoplasma gondii belongs to the so-called protozoa. These are de facto unicellular organisms, which, in contrast to bacteria, already have special features of "higher" cells. These are, for example, a cell nucleus, mitochondria, etc. [10]. You can imagine Toxoplasma gondii as some kind of amoeba.
The potential mind-altering capacity of toxoplasma was first demonstrated in rodents [19]. After infection of rodents with Toxoplasma, they were no longer afraid of cats. Further, the rodents no longer showed any reaction to the smell of cat urine (a typical alarm signal). Moreover, their ability to learn and remember was impaired. Concomitantly, they were increasingly hyperactive and "mindless". In short: They became easy prey of their predators.

After observations like this, it was suggested that Toxoplasma is also able to affect the human mind. But also before that, it was often assumed that aggressive, risk-taking and impulsive behavior could be associated with toxoplasmosis. The research of this subject ranged back into the early 90s. Eventually, in a review article from 2018, the authors made a comprehensive analysis of the available data [20]. To detect Toxoplasma you try to find antibodies against Toxoplasma gondii in the body of patients. The presence of antibodies indicates the presence of Toxoplasma gondii. The first problem in this context is that the mind-changing ability is highly dependent on the Toxoplasma strain [20]. Therefore, it is hard to distinguish between mind-altering and non-mind-altering Toxoplasmas. Furthermore, the detection methods became better and better in the last 30 years. That means some of the infections were probably hidden from the scientists' radar 30 years ago. Today, however, you will find them. Because of this reason, it is hard to compare results anno 1992 with those of today. Moreover, the human psyche is a really complex multi-faced continuum. Aggressive behavior does not necessarily correlate with "brain amoeba". In addition, the psychological evaluation has changed within the years and differs from country to country. Taken together, the authors of the above-mentioned study [20] conclude, that based on the current data, no alteration of the consciousness caused by Toxoplasma gondii in humans is provable.

Therefore, you can take your cat back into your house. But stay cautious!

1.8 Summary: Parasites, viruses & bacteria
There are certainly parasites & Co. that can trigger zombie-like behavior. Particularly affected are insects. In the case of humans, however, the efficiency of zombification is still very low. This also applies to other potentially viruses of humans such as the Zika viruses [21] or the rabies virus [22].

Thus the zombie apocalypse is postponed.

Option 2.: 2. Substances

It should be clear to everyone that certain substances "affect" their consumers mentally. But is this enough to turn them into zombies?

2.1 Synthetic cannabinoids
Synthetic cannabinoids and other drugs are causing tremendous health problems and even promote "zombie-like" behavior [8]. Initially, these substances were designed for the study of cannabinoid receptors in laboratories. However, rapidly they became a very popular drugs on the street. One of the first available products in 2008 was "Spice" or "K2". Since then plethora of modifications was released challenging authorities and physicians. The main problems are: 1. It is difficult for the authorities to prohibit the substances in time, 2. these dangerous substances are carelessly consumed and 3. the treatment of consumers is often difficult due to the lack of information/experience. Eventually, in 2016, a veritable zombie epidemic broke out, affecting over 30 people [8]. The symptoms were: A fixed gaze, lethargy, heavy sweating, and zombie-like moan. Nonetheless, their bodily function was remarkable "normal".

However, no violent behavior was observed (at least not in my research). Further, these substances are not contagious. Taken together, the definition of a zombie is not accomplished.

2.2 Flakka
Another case is Flakka. Flakka is a synthetic cathinone that promotes the release of dopamine while inhibiting its reuptake, as well as the uptake of serotonin [21]. As a result, the consumers have extreme feelings of happiness, an elevated drive, and better performance. Finally, they becoming crazy and aggressive. This aggressiveness can lead to extreme violence as occurred in Mallorca & Ibiza, as well as in Florida. The consumers of Flakka chased passersby and hurt them sometimes severe.

Although this sounds a lot like a zombie apocalypse, Flakka still does not meet the criteria. The reason: The symptoms are neither contagious nor long-lasting.

2.3 Medicines
Certain medications can also cause zombie-like behavior in overdose, abuse, misuse, or cross-reaction. To write about this is clearly out of the scope of this article. Especially, patients who are already suffering from neurological problems, such as in the case of dementia, seem to have a higher risk [7].

2.4 Zombie toxins
It seems like that there pronounced voodoo cult in Haiti. A researcher name Wade Davis has tried to investigate these phenomena in the early 1980s. His hypothesis was that "Voodoo powder" contaminated with puffer fish poison was responsible for zombie-like behavior. However, a subsequent study by the Havard University found that the concentration of these substances called tetrodotoxins was too low for any effect [23]. Even mice were extremely unimpressed by these doses. The cause of the voodoo phenomena is therefore still unclear. Maybe it has a psychological background [21].

2.5 Summary: Substances
Drugs are probably the most effective approaches to achieve human zombies. Nevertheless, a permanent exposure as a prerequisite, as well as the inability for transmission/propagation prevent the creation of "real" zombies.

Option 3. Other factors

In fact, there are other aspects to consider. Many people are probably familiar with the term Smombie. These are people who are so tied up by what's happening on their smartphones that they're walking around like zombies. I have to admit, that even I am also zombie-like sometimes, e.g.while being on the hunt for Pokemons.

Nonetheless, this consideration raises important questions. Is it possible, for example, to get brainwash by the media in such a way that you show zombie-like behavior? I have no idea about all the possibilities. The reading of Daniel Kahnemans book „Thinking, Fast and Slow“ [24], however, showed me some aspects of human suggestibility could well be used as tools for brainwashing.

Anyway, I do not think that this is ultimately suitable for the creation of zombies. Further, you have to take into account that this is not contagious.

In their article The Zombie Within [25], the authors Cristof Koch & Francis Crick discuss the possibilities that humans are already zombies. Or at least are humans not that dependent on their consciousness as expected. As an example, they talk about sleepwalkers. intriguingly, sleepwalkers even move furniture and driving by car. Further, a lot of reactions by the body and mind are not dependent on consciousness.

To what extent are we already zombies anyway? I don't know!

Which of these options is feasible to summon a zombie apocalypse, as shown in movies?

In movies, zombie apocalypses are usually triggered by infections or something similar. Often the zombies walk around and zombify healthy people, for example, by bites. Because of this, only Option 1 (parasites, viruses, and bacteria) would (almost) fit the criteria. Since I could not find any study on the design of brain parasites I assume no zombie apocalypse is scheduled. However, the fact that similar things were evolved in nature suggests a principle possibility. The use of mind-altering drugs would probably be easier but requires the constant exposure of humans to the drug. Therefore, a zombie apocalypse in this way demands many resources. Eventually, the perpetrator would end up either by poisoning themselves or not get everyone zombified. Therefore, I exclude a zombie apocalypse in this way. There remains Option 3 "Change of Consciousness through attention control". Even though I also turning into a zombie occasionally while playing Pokemon, I can't imagine that something like this would be possible.

Further, this would not fit into my criteria because of the lack of infectiousness. Therefore, I also exclude Option 3 as the basis for a zombie apocalypse.

So we have to note that only Option 1 could be a potentially sustainable concept for a zombie apocalypse. But even combinations of the Options, such as Flakka-producing Toxoplasmas are thinkable.

Let's assume that all the guidelines for a zombie apocalypse are accomplished. Now it has to be clarified if this would be successful at all. As a child of the 90s, I played Resident Evil 1. Already more than 20 years back, I always asked myself whether a zombie apocalypse would just fail because of the physical disadvantages of a zombie (short range, low speed, one-sided food preference, etc.).

By fulfilling all criteria: Would a zombie apocalyptic be successful, anyway?

In a great article by Alemi et al. 2015 [9] titled You Can Run, You Can Hide: The Epidemiology and Statistical Mechanics of Zombies, the authors built a mathematical model that simulates a zombie apocalypse. I can recommend everyone to look at the paper, it's really funny. The authors came to the conclusion that a zombie apocalypse would actually be successful. Initially, chaos would erupt primarily in urban regions. After a single week, all major cities would be taken over by zombies. Then the zombies would make their way to the periphery. Eventually, within about three months, the epidemic would be present in the entire state. In the end, only remote regions in Montana and Nevada stay zombie-free.

Fig.6 If it comes to the zombie apocalypse, our American friends stay safe in Montana and Nevada. Made by Chapper - unrestricted use allowed

According to Alemi et al. vaccinations, as well as the removal of the head, would be the most effective strategies to counteract a zombie apocalypse. However, the authors do not consider at this point that even the severe wounding would make the zombie unable to fight. As a "living being", also zombies depend on functioning muscles and cells, as well as an efficient cardiovascular system [26]. The zombies should, therefore, have supernatural abilities. Since we excluded sorcery as a zombie inductor, a zombie apocalypse would be much easier to stop than Alemi et al. 2015 suggest. It must also be considered that the zombies would soon starve to death because of their limited cognitive and intellectual abilities, without strategic concepts. For this reason, the campaign of the zombies would be 1. very disorganized, 2. it would be very easy to fight the zombies and 3. is attributed to a rapid stagnation of the zombie boom in a few days. Therefore, zombies could make chaos in big cities, but will never be successful nationwide.

In the article from Business Insider of 2016 they wrote about an alleged Pentagon strategy paper, which was supposedly designed for the case of a zombie apocalypse. However, I have strong doubts about the authenticity of this document. For instance, among others they talk about Space Zombies, Chicken Zombies and Evil Magic Zombies. If this plan (called CONPLAN 8888) should be real, the soundness of mind of the responsible people must be strongly doubted.

Nevertheless, the American authorities for health and emergency management indeed released a roadmap for prevention of a zombie apocalypse [27]. However, this campaign was just launched to make the people more aware of civil protection, e.g. in the case of hurricanes.

Summary.

Zombie-like creatures exist! However, not in a way as shown in movies or the video game [7 Days To Die] (https://www.amazon.de/7-Days-Die-PlayStation-4/dp/B01E6XUDIA). A zombie epidemic is difficult to implement and would not lead to the much-cited "zombie apocalypse".

Prerequisite for a successful zombie apocalypse would be sorcery which is possible in movies, books or video games but not in reality.

Although science deals with the topic zombie, however, this primarily serves to make the explanation of other phenomena a bit more tangible and understandable.

If you still fear the invasion of zombies, then buy [7 Days To Die] (https://www.amazon.de/7-Days-Die-PlayStation-4/dp/B01E6XUDIA) and practice the emergency…

… or do Steemit!

Have a nice week

Regards

Chapper

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