This analysis is inspired by a post by @carlatsukinamistolemyhamsandwich and how Endzeit is never specified as a virus - yet we all seem to refer to it as one. It peaked my interest since I never really noticed it when playing through the games, and once she pointed that out, I thought I’d do a little digging.
Regarding Endzeit, it's never mentioned what it specifically is - we're only led to believe it's a virus, yet it is never specified in any route; it's simply known as a "disease". So, using a little biology, why not figure out what kind of disease Endzeit actually is ?
For specification purposes, I'm only going to focus on how it's transmitted and affects cells, rather than analyse any symptoms it causes. This is due to the Diabolik Lovers universe being fictional; therefore, any symptom can be purely fictitious. For example, you could contract a disease that turns your skin green or gives you purple eyes - however, when defining what type of disease it is, those symptoms don't matter (they're made up) whereas the transmission of that disease does matter. There's only a set amount of ways a disease can be passed on: through skin contact, blood, ingestion and water contamination, and those transmissions can be analysed and lead us to our answer.
Infectious illnesses, deficiency diseases, hereditary diseases (covering both genetic disorders and non-genetic hereditary diseases), and physiological diseases are the four primary categories of disease. Other categories of sickness exist as well, such as communicable and non-communicable diseases. The most fatal conditions in people include lower respiratory infections, cerebrovascular illness, and coronary artery disease.
Though it never states that Endzeit is a virus, we learn that Endzeit is transferred through blood contact. So if we go off the basis of the main types of diseases: parasites, bacteria, fungi, and viruses, we can narrow down our options and find out what Endzeit truly is.
So, shall we begin ?
Word Count: 2,461
Let's begin with fungal infections and how fungi compares to Endzeit. Fungus is a collection of microorganisms that belong to its own kingdom and are neither plants nor animals. Fungi are widespread in nature and may be found on human skin, in the soil, on plants and trees, as well as on numerous interior surfaces. By dispersing tiny spores, fungi proliferate. These spores are frequently found in the soil and air, where they can touch surfaces of the body, especially the skin, or be breathed. These fungi develop, disseminate, infiltrate tissue, and spread locally when fungi enter the body and the immune system is suppressed. Some organisms, particularly yeast and some moulds, have the ability to enter blood arteries and infect nearby organs as well as the circulation.
Direct skin-to-skin contact (with people or animals) or indirect contact with infected objects on floors or in the ground are the two main ways that fungal infections spread. With the way Endzeit acts and transmits, we can easily list fungi off our candidate list since fungal infections are caught through skin-to-skin contact and not through blood as we see with Endzeit.
Next to dissect are parasites. A parasite is a living thing that inhabits its host and feeds off of or at the expense of it. Protozoa, helminths, and ectoparasites are the three primary groups of parasites that may harm humans. A parasite consumes components or essential substances from its host, another living thing. The host can suffer certain effects of the parasites - hiwever, they do not instantly or even ever kill the creatures they use as food, in contrast to predators. Although dangerous bacteria and viruses also live as parasites, parasites are eukaryotic creatures. Plants, animals, or fungi can all be parasites.
Transient parasites make contact with the host, but only to feed from it. The blood-sucking bats of South America and mosquitoes are two examples of transient parasites. In addition to using the host as a source of food, persistent parasites also use it as a home. Permanent parasites include hookworms and tapeworms. The parasite may be found in the bloodstreams of those who have it, and contact with the blood of an infected person has the potential to spread the parasite to others (for example, by blood transfusion or by sharing needles or syringes contaminated with blood).
As far as we know from Carla's routes, Endzeit is a blood disease that is transmitted through blood contact; implying that it infects other blood cells in order to break down the body. Endzeit attacks the blood. However, a parasite is an organism that feeds on parts or vital products from another living organism. Endzeit in itself isn't alive whereas parasites are - they usually come in the form of tapeworms that can also infect the blood. Parasites can be microscopic or large enough to see with the naked eye, and they survive by feeding on the host. They can also spread parasitic infections, which can lead to sepsis.
Ectoparasites like lice and mites can adhere to or burrow into the skin and remain there for a long time, whereas protozoa and helminths mostly harm the stomach. Most protozoa and helminths are either extremely mildly unwell or non-pathogenic, which means they don't cause disease. The most typical method of passing parasitic protozoa and helminths from person to person is by faecal-oral transmission, in which parasites discovered in one person's stool ends up being ingested by another organism. Diarrhoea and other gastrointestinal issues are frequently the first signs and symptoms. The effects might get worse when parasites attack the organs or red blood cells.
Bacteria and viruses can live outside of the human body - parasites, however, require a living host in order to survive. Bacteria and parasites can usually be destroyed with antibiotics. On the other hand, antibiotics cannot kill viruses. Bacteria, viruses and parasites can cause a wide variety of illnesses and can infect any of the organs of the body. Viruses are often responsible for respiratory illnesses and digestive illnesses. Bacteria can infect any part of the body, but often cause diarrhoea when they invade the digestive tract.
The one glaring hole in this contender is how parasites are caught - parasites are ingested through contaminated food or water. We know that Krone was locked in the dungeon after being infected with Endzeit and that Carla looked after her; therefore, they would have been exposed to the same drinking water and food, yet Carla is not affected by water or food - he's perfectly fine. My point is that parasites travel and infect through ingestion - they use water and food to gain a host; regarding Carla and Giesbach at this time, neither of them are infected, even when they most likely drank the same water as the infected. So that means that Endzeit couldn't have infected the Founders through ingestion or water; therefore, Endzeit is not a parasite either.
Bacteria is made up of a single complicated cell. It has the ability to endure on its own, within or outside of the body. Most germs don't cause harm. In actuality, our bodies contain a variety of bacteria, particularly in the stomach where they aid in food digestion. Some germs, however, can lead to illnesses. Bacterial infections can damage the skin, stomach, lungs, throat, and many other body parts. Many are minor; a few are serious.
A person's health is significantly impacted by bacterial illnesses. Any part of the body can develop the disease, and it can be brought on by the organism itself or by the body's reaction to its presence. Humans can contract bacteria via the air, water, food, or living things. The main means of bacterial infection transmission include contact, aerosol, droplets, vectors, and moving vehicles.
When germs that cause an illness in another region of your body enter your circulation, blood poisoning ensues. Septicaemia or bacteraemia are terms used to describe the presence of bacteria in the blood. Although they aren't nearly the same, the phrases "septicaemia" and "sepsis" are sometimes used interchangeably. Sepsis may result from septicaemia, the presence of germs in the blood. If untreated, sepsis is a serious and frequently fatal illness condition.
The most important part here is that bacteria acts the same way as parasites in regards to their transmission; it doesn't spread through blood contact. This means that Endzeit cannot be a bacterial disease.
Viruses hurt people by killing cells or obstructing cell function. Our systems typically respond by raising our body temperature, releasing a chemical called interferon (which stops viruses from multiplying), or activating immune system cells and antibodies to fight the intruder.
Viruses, which are nothing more than genetic material encased in protein, are the most basic kind of germs. A virus cannot function alone; in order to accomplish its single goal of replication, it must infiltrate a living being. A virus that enters a person's body has the potential to exploit the cellular machinery to replicate itself, take over new cells, and continue to spread. Also susceptible to infection by viruses are bacteria, fungi, and other living things. The virus starts to damage the body when it reproduces more quickly than the immune system can stop it. Since viruses are the tiniest germs and may move through the air with a cough or sneeze, they are typically the simplest to get. Some viruses can also transmit through body fluids or insects.
The biggest viruses are smaller than the tiniest bacteria, proving that viruses are smaller. Their only genetic components are a protein coat and a DNA or RNA core. They must cling to cells in order to replicate. Most of the time, they rewire the cells to produce fresh viruses until the cells rupture and die. Other times, they transform healthy cells into cancerous or malignant ones. Most viruses, unlike bacteria, do cause illness, and they target particular types of cells while doing so. For instance, some viruses target blood, liver, or respiratory system cells; sometimes viruses specifically target bacteria.
Blood contact or fluid-contact contracted diseases (such as Endzeit) are referred to as viruses. Diseases like Hepatitis and HIV are both named viruses and are spread through blood contact. The infected blood itself could arise from any of the disease types; however, Endzeit is spread through direct blood contact, which would effectively make it akin to HIV; therefore, it would be akin to a virus. Nevertheless, that's just the transmission, not the source - so for blood diseases to occur, there has to be something akin to impure or unclean blood, meaning that it's a bloodborne disease.
Bloodborne diseases are caused by pathogenic microorganisms, which exist in blood and other body fluids. Bloodborne pathogens are microorganisms such as viruses or bacteria that are carried in the blood and can cause disease in people. If Endzeit started as a bloodborne disease then it could have been caused by any of the disease types (if an open wound was infected by unclean air, bacteria, or fungi for example). However, for a bloodborne disease to spread, it must be through direct contact with the blood, and Endzeit is passed through direct contact with the infected blood, effectively making it a virus.
Additionally, Endzeit isn't caught through normal contact, it's just blood. So that means it transmits through DNA. In Carla's Labyrinth Ending in Chaos Lineage, we get the dialogue "Shin was exposed to Carla's blood at that time. Endzeit that only the founders can get, is passed by blood infections".
Viruses with a DNA core are capable of surviving in the nucleus of the cell they infect, using the host's biochemical machinery to replicate their DNA. The DNA of some viruses can become integrated into the DNA of the host cell. This means that the more the disease replicates, the worse the symptoms become, which could explain why Krone and Carla seem to have survived longer than the other infected founders - and again, this mainly arises with viruses.
Furthermore, we learn that Endzeit can be cured, but only if the founder becomes a ghoul - which means that the DNA must change. So the Endzeit must attack and infiltrate the DNA otherwise the DNA wouldn't need to change, and what specifically attacks and infiltrates cell DNA? A virus. A DNA-dependent DNA polymerase is used by DNA viruses to copy their genetic material, which is DNA. The nucleic acid is primarily dsDNA; ssDNA is less frequent since ssDNA often expands to dsDNA during replication. This would explain why Endzeit can only be transmitted through blood and why it attacks the body as it does - by replicating its own DNA, it kills the host's cells in the process.
When a virus attacks a cell, it replicates its own DNA until the original cell bursts; this would naturally explain the tamer symptoms we see Carla experience such as blood spots. The closest disease to the blood spots we see is called purpura. Purpura, also called blood spots or skin haemorrhages, refers to purple-coloured spots that are most recognizable on the skin. The spots may also appear on organs or mucous membranes, including the membranes on the inside of the mouth. Purpura occurs when small blood vessels burst, causing blood to pool under the skin; it’s also caused by viruses such as HIV and Hepatitis - which are bloodborne viruses.
Although it's said that the founders believed it to be airborne (and it very well could have started like that) from what we see with Carla, if it was still an airborne disease, Shin should have caught it. This is due to the fact that the two are accompanied by one another and also share physical contact such as when Carla strangled Shin or even just the fact that they are close together. The fact that this does not occur and that Shin has an 'immunity' to Endzeit means that it must have mutated at one point inside one of the founders, making it a bloodborne virus and not airborne bacteria since the Endzeit can only be passed on through blood contact, which is what we see both within the Labyrinth Ending and back in Banmaden when Carla and Krone were locked away.
Moreover, Menae also escaped Banmaden, meaning that if it was airborne, there would be a chance of her being a carrier; from what we see, she never caught or carried Endzeit. So there has to have been a mutation within one of the infected founders' cell DNA; thereby making it a transmuted virus as opposed to an airborne or bacterial infection. Bacteria doesn't attack the cell or the cell DNA, so the symptoms we see (blood spots, bruising and coughing) shouldn't be caused by airborne bacteria - but that's taking the disease at its closest comparison; we have to remember that this disease is fictional - the most important factor is the disease's transmission. Endzeit is transmitted through blood and blood alone; thereby naming it a DNA virus.
In conclusion, though it's never stated as a virus, the Endzeit itself has all the transmission and developmental qualities of a virus - specifically a bloodborne DNA virus as opposed to a fungal, bacterial or parasitic disease.