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In my fantasy world vampires exist, and most of the intelligent races can be turned into one. I try to make everything in this word kind of explainable by science, at least possible in our Earth.

I've encountered a problem: how would vampires avoid catching diseases when ingesting blood? Vampirism is a virus that can spread by blood and saliva, but if vampires needed the intelligent race's blood to survive, they would easily contract blood transmitted diseases. This would make it extremely hard for them to survive. A bit about my vampires:

  • If you survive a vampire bite, you will probably become one.
  • Vampires don't live longer than normal. They live as long as they would if they weren't infected.
  • Vampirism is a virus.
  • There is a slow transformation a vampire has to endure, like canines falling one by one and larger ones growing in their place.
  • They can't survive just on blood, they need other things too, but the virus demands blood.
  • They can barely survive by drinking animal blood.

Would this type of vampire be viable? And what's a thing that could protect them from getting terribly ill by drinking a normal meal?

Edit: Yes, by them getting ill I mean by illnesses carried by the bitten ones, and the vampires are still alive and their bodies work very much like they did before the virus, the only main changes are on the digestive system.

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    $\begingroup$ Do you mean getting infections carried by the bitten one? Or food poisoning? $\endgroup$ – L.Dutch - Reinstate Monica Jul 9 at 15:43
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    $\begingroup$ Am I correctly understanding that your vampires a still alive, all the same biological processes are still occurring just as they did when they were a normal human? $\endgroup$ – Morris The Cat Jul 9 at 15:44
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    $\begingroup$ You seem to be asking 2 questions: one: can viral vampires contract diseases from infected blood and two: is your viral vampire viable (YAY alliteration!) $\endgroup$ – CaM Jul 9 at 16:06
  • $\begingroup$ They have a more powerful stomach than humans, which is strong enough to digest any disease causing microorganisms. $\endgroup$ – alexgbelov Jul 9 at 23:01
  • $\begingroup$ This question reminds me of the rabies virus. Horrifying. $\endgroup$ – cst1992 Jul 11 at 9:19

11 Answers 11

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The Vampire Virus is ferociously territorial.

However, another immune cell specialises in killing cells that have a reduced number of MHC class I molecules on their surface – this cell is a natural killer cell or NK cell for short. When the NK cell finds a cell displaying fewer than normal MHC molecules it releases toxic substances, in a similar way to cytotoxic T cells, which kill the virally-infected cell.

Once infected, the host's immune system is modified to ignore the Vampire virus itself, but in order to ensure survival of the host, the Vampire Virus dramatically enhances the host's production of Natural Killer cells, as well as other parts of the host's immune system, to ensure that any competing viruses or bacterial infections are annihilated before they can compromise the host's ability to continue spreading the vampire virus.

https://www.immunology.org/public-information/bitesized-immunology/pat%C3%B3genos-y-enfermedades/immune-responses-viruses

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    $\begingroup$ This may keep the host free of disease, but with a hyperactive immune system, quickly killing off potentially infected cells, the host body may be in a constant state of decay as the time to replace cells is longer than the enhanced immune systems cell destruction time. $\endgroup$ – Sonvar Jul 10 at 3:20
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    $\begingroup$ @Sonvar That would explain why the vampires sleep soo much (like, all day and most of the night!?). So their tissues have time to recorver. That would also explain why they all look like trash: ill-white, deep eye sacks, dry and wrinkly skin, all look elderly... It's the toll of living with cells replacing themselves at a stressful rate. $\endgroup$ – Oxy Jul 10 at 7:54
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    $\begingroup$ Autoinmune syndromes and allergies would be extremely lethal, though. $\endgroup$ – Rekesoft Jul 10 at 8:51
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    $\begingroup$ Allergies being lethal could make for a good plot point, actually. Some people might just not survive the process of becoming a vampire. $\endgroup$ – Hugo Zink Jul 10 at 14:28
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    $\begingroup$ @HugoZink Allergies like [insert giant list of folkloric vampire countermeasures here], you mean? $\endgroup$ – Alex P Jul 10 at 22:39
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Vampire biology is significantly different from other species

Every disease requires specific host attributes to reproduce and thrive. If the disease's requirements aren't met, it can't grow/spread. By altering the vampire's biochemistry, the new vampire becomes highly inhospitable to any bacterial or viral diseases that were afflicting it before transformation. We see example of this kind of selectivity in bacteriophages. Bacteriophages will attack specific bacteria and only those bacteria, thus making them safe to treat humans.

There are number of ways that the vampire's biochemistry can change to make it inhospitable to diseases from lesser lifeforms.

High Salt Blood

For example, let's say vampire blood is extra salty at 3.5% (similar to sea water). Normal human blood is 0.9% salt. A bacterial infection accustomed to low salt then thrust into a high salt environment is going to have a really hard time. Some bacteria would be able to survive the transformation but not many.

Cellular Receptor Changes

Another approach might be to have the vampire virus rebuild the receptors on the host's cell walls. Without those receptors, the usual entry points bacteria and virus aren't there anymore.

Gram-Negative Cell Walls

Or, the vampire virus changes the host's cellular structure to be gram-negative. Examples of diseases caused by gram-negative bacteria include leprosy, tuberculosis, Lyme disease; all very hard to treat. If a vampire's basic biology shifted to being gram-negative, this gives the double benefit of being effectively incurable and also very hard to kill by poisons.

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    $\begingroup$ could also have the result vampiric biology be similar enough to be a carrier for blood born diseases but not vulnerable to them in the same way a rat may carry bubonic plague but not be affected by it $\endgroup$ – BKlassen Jul 9 at 16:01
  • $\begingroup$ @BKlassen Easily. $\endgroup$ – Green Jul 9 at 16:03
  • $\begingroup$ You forgot the obvious change: Temperature. Traditional undead vampires are generally cold (unless they've recently fed); if the virus version also lowers operating temperature, then they'll be pretty inhospitable to human diseases. Most human-targeting diseases operate at human body temp (give or take a few degrees). Drop the temperature to 90 or lower, and you're not even close to what they can function at. $\endgroup$ – ShadowRanger Jul 11 at 15:25
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This is not really a problem. Blood does not carry a large number of pathogens and your stomach acid and immune system are quite capable of dealing with those that do arise.

I like a rare steak as much as the next person, the centre of the steak has uncooked blood myoglobin and this is safe, there are very few pathogens in blood (or myoglobin). Steak should be seared on the outside to kill bacteria on the surface, those bacteria have usually got onto the meat in the slaughter and handling process. The inside is clean.

If a vampire does bite someone with a blood-borne illness, like HIV, there still should be no problem. The blood will go to the stomach get mixed with acids, which kill most pathogens, through the intestine and out the end. Any pathogens that survive the stomach and intestinal enzymes will get excreted as there is no direct contact between the contents of our intestine and the blood. A few specialist bacteria can survive process of being eaten, but these are gut specialists.

If any pathogens do somehow manage to get past all these lines of defence, then the usual immune system can remove any that get into the blood. But there are probably far more bacteria on the surface of the apple that the vampire has for desert, than in the blood of the victim.

So there is no real danger of vampires from pathogens in blood, because there aren't any.

(regarding the fact that blood contains nothing special that other food doesn't contain: The virus changes behaviour to cause a blood obsession. It does this purely to spread through infected saliva. So vampires don't need blood, but they think they do because the virus has infected their brain)

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    $\begingroup$ which kinda puts the lie to vampires requiring blood as a part of their diet as blood contains nothing special after digestion that can't be obtained from other sources of animal protein like meat :) $\endgroup$ – jwenting Jul 10 at 7:35
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    $\begingroup$ The pink-red liquid seeping out of the center of a rare steak is not blood, it's myoglobin. Blood looks VERY different - by the time it can get to your table, it's very dark red and very thick. With a bit of heat, near black and solid. $\endgroup$ – Therac Jul 10 at 9:58
  • $\begingroup$ Hmm, blood pudding for breakfast. $\endgroup$ – James K Jul 10 at 16:34
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    $\begingroup$ You absolutely can get sick from drinking infected blood. I would imagine hepatitis, ebola, HIV, and/or parasites would be transmittable through consumption of infected blood. See this study about the consumption of raw pig blood (not myoglobin): wwwnc.cdc.gov/eid/article/20/11/14-0915_article $\endgroup$ – Mike D. Jul 11 at 9:26
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    $\begingroup$ also, the statement "no real danger...from pathogens in the blood, because there aren't any" is false. 'There are 26 different viruses that have been shown to present in healthcare workers as a result of occupational exposure. The most common bloodborne diseases are hepatitis B (HBV), hepatitis C (HCV), and human immunodeficiency virus (HIV). Exposure is possible through blood of an infected patient splashing onto mucous membranes...' - like inside your mouth. en.wikipedia.org/wiki/Blood-borne_disease $\endgroup$ – Mike D. Jul 11 at 9:26
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Cook the blood

Why searching for complicated biological solution ? As you not specify that vampire need freshblood, the vampire may, as normal human, cook their meals. This is the oldest way to prevent illness from food to happen. Will you ever consider eating raw pork meat? No, because you know it will get you parasites and all this kind of stuff.

They may for example made a blood soup with vegetables to get all the nutrient they need. More important, cooking, by linking the proteins, increases digestability and assimilation of the blood nutrient. They will bite only on selected target to contaminate them to avoid disease transmission like @Willk pointed it out. Nowadays human do that: for example, cow meat doesn't contain much parasites and bacteries, so some people like it raw and may enjoy it without much illness risk.

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They choose their victims carefully.

A desperate vampire will bite whatever it can catch. Maybe this will be someone slow and diseased and the vampire might catch the disease. The stomach is pretty good at killing ingested pathogens - for example you would not get HIV from drinking blood but you might get syphilis on your mouth if you bit someone with sores on their skin. If you had syphilis sores on your mouth you could then catch HIV or hepatitis thru the sores. Desperate vampires become diseased vampires, who then become more desperate. Good stuff for stories!

A vampire with choices will choose its victim carefully. It will not want prostitutes or dissolute sickly folks. It will want young people who look healthy, with healthy habits. It needs to balance the youth and good health of the victim against the fact that the victim might effectively fight back and get away, or live with people who can readily come to his/her aid. These vampires might watch for some days before deciding on a victim.

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Answer is pretty simple

  • Viruses are capable of mutating DNA
  • Only certain animal species are vulnerable to specific virus strains (swine flu/mad cow disease not affecting other animals without having the virus mutate)

So all you need is your vampire virus to mutate the DNA of the host enough to change it into another species that is different enough from humans that the traditional viruses cannot take root and multiply. In most cases you can handwave the specifics because science supports the fact that most viruses are targeted to specific species.

There are very few viruses that are cross species, but one example is the Bird Flu (H5N1) which can be deadly for most mammals including cases with humans, dogs, cats, etc.

Now it would be very possible for the human scientists to genetically engineer a virus that targets vampires only and might even be a variation of a deadly human virus such as small pox. Another possibility is a virus that can neutralize the vampire virus (viruses can target viruses too).

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  • $\begingroup$ To be precise, only a specific type of viruses modify DNA: the retroviruses, like HIV. Regular viruses tend to just modify RNA, to made the host cell produce its own protein. $\endgroup$ – Cailloumax Jul 10 at 9:27
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Their immune system gets ridiculously strong

Just like with snake poison, where you can ingest tiny amounts of it every day to become immune, your vampires ingested tiny amounts of viruses and bacteria every time they drink some blood, resulting in an overall stronger immune system.

https://www.theguardian.com/environment/2018/feb/11/poison-pass-the-man-who-became-immune-to-snake-venom-steve-ludwin

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My answer is similar to @Philipp's but it is to do with vultures

Dr. Dayton writes:

"The main reason vultures can eat almost anything is that they have the lowest gastric pH in the animal kingdom. Stomach acid protects all animals because it digests bacteria and other living organisms along with other proteins. Human stomach acid has a pH of 2. It kills 99 percent of bacteria in contact with it, but people still get sick and can die if they eat enough contaminated or rotten food.

"Turkey vultures’ stomach acid has a pH slightly above zero, lower than car battery acid and 100 times as concentrated as human gastric juice. It can dissolve metal, e.g. shovels, as well as digest nearly all organisms, including those that cause botulism, anthrax, rabies, cholera, hepatitis, and polio, along with other proteins. Vultures can eat just about anything that is dead and rotten, including animals that died from infections that, in turn, would kill most people who ate them.

vulture stomach acid

So the vampire virus makes your stomach work and act like a vulture, just don't be sick or it will eat your mouth and throat.

It also make you very very anaemic, and like pregnant women sometimes crave weird food, they don't actually NEED blood, but wow do they want it.
Imagine an alcoholic on a brewery tour, that is a vampire walking around all day.

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Vampirism is a virus

The virus, by integrating in the vampire's DNA, alters also the expression of the surface receptors of his/her cells. Altering this surface receptors means that most if not all of the pathogen agents have no longer the key to open the cell door and infect it.

This makes the infected immune to any disease carried by the dinner.

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    $\begingroup$ This helps against viral diseases (such as HIV) but not against bacterial infections (such as syphilis). $\endgroup$ – Renan Jul 9 at 17:24
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Vampires are usually old

In a medieval place, if you have lived long enough, you've had contact with lots of diseases - and survived them all. There is no better vaccination than surviving thriugh an illness.

It used to be that parents would expose their kids to other kids with chickenpox so that the children would develop immunity against that earlier.

So in a fantasy setting, if someone over 60 is walking and breathing, they surely have antibodies acainst evetything.

Cure potion

No fantasy setting is complete without panacea in a bottle.

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  • $\begingroup$ Yes but vampires eat blood. They wouldn't only have a chance to contract the disease, they would be directly exposing themselves to it, and a lot of illnesses are deadly and have no cure. $\endgroup$ – Onix Jul 9 at 17:32
  • $\begingroup$ @Onix, what if the vampire virus caused your own immune system to acquire the characteristics of the host? The more blood you drink, the better the reception—which encourages them to drink more—where drinking little would mean you were more likely to contract diseases. This is assuming the host has built an immunity. $\endgroup$ – Nathan Goings Jul 10 at 2:46
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Their stomach acid is antibiotic and antiviral.

When they drink blood, that blood mixes with their stomach acid and gets sterilized.

A possible other infection vector could be blood-to-blood infection in case the vampire has small injuries in their mouth, throat or esophagus. The superhuman resilience to injury attributed to most fictional depictions of vampires could help here.

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