What disease affects only the non-peasants?

Question

Imagine a roughly medieval world with a feudal government.

I want a new disease to show up and spread rapidly which affects the nobility and leaders, but not the peasantry, setting up a situation for the feudal system to be overthrown.

The disease should not be magical, should be either fatal or at least highly debilitating, and must affect the nobles and royalty. I'd sort of prefer it to affect solders and possible merchant and clergy class as well, but what I most care about is that the nobles and leaders are affected. Finally, as said, the peasantry should be mostly unaffected, or suffer significantly less drastic symptoms if affected.

Former peasants that take on a position of power after the former government collapses shouldn't immediately be set upon by the same disease, whether this is because they continue to maintain whatever cultural or environmental habits inoculated them before they rose to power or the disease has simply run its course and died out due to herd immunity once all the nobles are gone doesn't matter.

Ideally the disease has/will manage to continue to move from country to country, destabilizing ruling bodies as it goes. In a perfect world it would move between countries slowly enough for countries to already have heard about and fear (or look forward to, depending on your class...) the disease by the time it reaches them, but this is less important.

Edit: To make it clear I realize that no disease is exact. While I say the disease should attack nobles and not peasant in reality it will likely kill plenty of peasants and miss some nobles. I want only that, in general, the noble class suffers far worse then the peasant class due to the disease.

What kind of disease could behave like this, and what is it about the peasant lifestyle the protects them from it?

Answer 1

Spices

Spices were rare, expensive, and prestigious. A powerful merchant class has found a new spice, and its use spreads rapidly because, like all spices, it is light and easy to carry, with much value per ounce.

It's also a cumulative poison.

Additional rumors that it has magical properties that will bring power to the bearer will cut down on the giving of the scraps to the poor -- at least the scraps containing this spice.

If you like, you can specify that it weakens the immune system so that people die of different diseases, making it harder to trace.

Answer 2

Proximity to Animals Vaccinates Peasants

Small pox was like this. Milkmaids had exposure to cow pox, so were somewhat immune to the more dangerous small pox. If there were a deadly disease (like small pox) only found in humans, but a less deadly, related, disease was already common in farm animals, the same situation could arise, but with the prior exposure not limited a smaller group such as milkmaids. As peasants interact with animals regularly, they might have some form of immunity to the more dangerous disease which the nobility lack because they do not interact with farm animals.

Answer 3

Gout

Known historically as the disease of kings, identified by the Egyptians in 2640 BC, and listed in the Ebers Papyrus (1500BC).

It's basically caused by eating too much rich food over a long period, hence it was a disease of the wealthy, cost of food being a limiting factor to the poor. Nowadays it's a disease of the poor, as the wealthy have access to better nutrition, but that's not under consideration here.

For your purposes, your ex-peasants are likely to avoid getting fat as a matter of principle and hence not suffer for the first generation of becoming wealthy.

Answer 4

Create an expensive but toxic fad

It was common in the 16^th century for especially west-European nobility to paint their faces with substances containing lead, in order to appear as white as possible to distinguish themselves from the peasants, who had to work in the fields under the sun.

An example of one of these face whiteners is Venetian ceruse, which

consisted of a lead and vinegar mixture, known to cause hair loss, skin corrosion, muscle paralysis, tooth deterioration, blindness, and premature aging. Venetian ceruse was also reported as a source of lead poisoning. Lye and ammonia, found in other skin whiteners, compounded the toxic effects of lead. Other practices done in the name of skin whitening included washing one's face in urine and ingesting wafers of arsenic.
^source

People are capable of sacrificing a lot in their attempt to look better, which can be used to your advantage.

Answer 5

You may want to look into beriberi for inspiration!

It is a disease caused by a Thiamin (vitamin B1) deficiency, and primarily affected people whose diet consisted of mostly white rice or highly refined carbohydrates.

Rice with a lot of bran and hulls (peasant food) still had the vitamin, but the "pristine" rice actually lacked it. There were historical cases in Asia during wartime when a large number of the defending forces were suffering from the disease, yet the prisoners didn't as they had been eating the cheaper, less refined rice. The disease was partially identified when the released prisoners were given white rice and began to suffer the disease too. Today's rice and other cereals are enriched post-processing to prevent this, and you can also get the vitamin from the following:

• Pork
• Fish
• Legumes
• Peas
• Sunflower seeds
• Yogurt

However, "Thiamin can be destroyed with high-heat cooking or long cooking times. It also leaches into water and will be lost in any cooking or soaking water that is thrown out." [1]

In a setting without modern knowledge of nutrition, anyone with two coins to rub together would rather eat highly refined and pretty carbohydrates, while only the poor would have to settle with the unrefined, gritty, crunchy stuff that sticks in your teeth even after cooking.

In summary, all you need to do is take a staple food, introduce a suddenly popular and novel way to make it more refined, and have it turn out that a vital nutrient not supplied elsewhere in the diet is now missing.

Answer 6

The only thing I could think of is if a special commodity that they didn't know was actually poisonous. Similar to the Chinese alchemy elixir poisoning, which claimed the lives of many Chinese emperors from 210 BC to 1735 AD (the elixirs, ironically drunk to obtain Immortality, contained Arsenic and Mercury). So if it was something the nobles and rich consumed but the peasants could not, it could be that was the source of the disease (especially if laws restricted the access to the this commodity so it was illegal for peasants to partake anyway, though again, Nobility does not equate to Wealth and vice versa).

Other than that, historically, wealth typically correlated with health, as those with money could afford to pay doctors for better treatments. That said, among European Nobility inbreeding was quite common and put many royals at increased risk for genetic diseases, but this wasn't a common symptomology. The hemophilia that famously brought Rasputin to a position of good graces with the Tsars was known as "The Royal Disease" due to how many royal families in Europe were susceptible to the genetic disease. This would only affect the nobility but not the wealthy non-nobles to such a degree.

There is very little in the way of biological illnesses, however, that could affect only a class of people since genetics is not an indicator of wealth.

Answer 7

Target behavior, not genetics

There are numerous maladies that are peculiar to the wealthy of that period. Gout and tooth decay come to mind. They figured out that doctors need to wash their hands because the women who could afford hospitals had a higher risk of dying in child birth.

You want something contagious, though. Come up with something that thrives unusually well in the world of comfort.

Immunity through labor

Alternatively, consider that milk maids were rarely killed by smallpox because they usually got cowpox first. maybe your world has an effective but expensive method of killing off fleas, and fleas carry something that inoculates people against bubonic plague.

Immunity through diet

Beriberi is something we don't think about much anymore. It got worse after the rice-hulling machine was invented. You could readily come up with a disease that hit the wealthy harder because of a favored food processing step that removed an essential vitamin.

Temperature based outgassing

Ok, here's one if you want the death to happen quickly, in a single instance. Let's say that there's a particularly vibrant paint that becomes extremely popular as wallpaper or rugs. The problem is that, when heated, it releases poisonous gas. Nobody notices for maybe a decade, until a heat wave blankets the country. Everybody in the castle dies one day.

If you haven't played Plague, Inc. yet, I recommend it. It'll give you a few ideas for pathways of transmission.

Answer 8

The disease causes a severe allergy to something noble-associated.

Everyone has the same two-week course of feeling lousy when they get the disease. Unpleasant, but rarely fatal and soon recovered from. But when the virus has left the body, the antibodies remain. Ever afterwards, if you breathe deep near a hawk's feathers your airway will close in anaphylactic shock: disabling and potentially fatal.

For peasants, this is no big deal. Wild hawks avoid humans and tame hawks are only legal for nobles anyway.

But for nobles, hunting with tame hawks is a critical part of court life. It'd be political suicide to abstain.

How realistic is this? Immunologists disagree on how common virus-triggered allergies are, but they're certainly possible. I think I remember at least one medieval European country had strict rules about which levels of nobility could use which birds in falconry, with peasants permitted none regardless of wealth, but I can't find the link now.

Answer 9

Make it a genetic disease.

The disease is passed on through inheritance rather than contagion. I realize this may not fulfill your requirements of a disease that quickly spreads from place to place. But it is the only one guaranteed to affect nobles and royalty only. Because of inbreeding, it can be passed down to nearly the entire next generation of nobles and the very rich. Maybe even some soldiers/merchant/clergy who have had children with nobility.

Such was the case with hemophilia in the 19th and 20th centuries:

Hemophilia has been called a "royal disease". This is because the hemophilia gene was passed from Queen Victoria, who became Queen of England in 1837, to the ruling families of Russia, Spain, and Germany. Queen Victoria's gene for hemophilia was caused by spontaneous mutation.

Because nobility often married second/third-degree relatives, hemophilia (a recessive, X-linked trait) was expressed in many of their children. But you can do better. Make the trait dominant. This way it will spread to most, if not all, of their offspring. Plus, princesses are often married off to royalty of neighboring countries in order to strengthen alliances, so the disease could be easily spread. It could be fatal or just highly debilitating depending on your preference.

This would make the upper class ripe for a takeover.

Answer 10

Scurvy

The nobles get to choose what they eat. White bread and meat and alcohol for every meal. The nobles are rancid with vitamin deficiency.

Eating Plants? Plants! Those green things that grow in excrement!? What do you take me for, a lowly peasant? Leave my manor at once, thy foul reprobate! Down the corridor, fourth door on the left, up the spiral staircase, across the courtyard. . . .

The noble diet is a more expensive version of the sailor diet. Sailors were historically plagued by vitamin deficiency that killed them or drove them mad. It took hundreds of years to find the cause.

The peasants are perfectly healthy. They eat whatever they can get or grow. Meat is expensive. White bread is throwing out half the grain. The peasants eat brown bread and fruit and vegetables and potatoes and milk and cheese. They eat some meat during the winter but they eat other things too.

The nobles are rancid with vitamin deficiency. The peasants are fine.

Edit:

I want a new disease to show up and spread rapidly which affects the nobility and leaders, but not the peasantry, setting up a situation for the feudal system to be overthrown.

What actually happened was a sudden frost killed all the rosehip plants in the country. Rosehip tea was the sole source of vitamin C for nobles. With that gone they start dropping like flies.

They did not notice the correlation because (a) the frost also damaged other crops and (b) a weekly cup of rosehip tea is not missed.

Scurvy Mouth from Science Photo Library

Answer 11

Mad King Disease

Whoops! It turns out that imported food (wine, meat, corn) is diseased this year.

The wine has lead acetate in it - lead acetate tastes wonderful, btw, very sweet. Maybe the corn has some nasty alkaloids. Gruesomest of all, the meat has prions in it, leading the wealthy and powerful to go mad before they go dead.

Peasants are protected from Mad King disease by being far too poor to import anything.

STIs

This year's plague's painful boils are extra painful because of where they grow. Soft tissues in dark places.

Male peasants are protected because they don't get to have sex with duchesses. Female peasants are still mostly protected but not 100%.

Addiction

Speaking of imports, all this heroin from India doesn't grow locally. Or maybe it's a snorted drug.

Did I mention peasants are too poor to import food? There's no way, none, nada, that Count Junky is sharing his stash with you, villein!

Answer 12

Chronic Wasting Disease is a prion disease in deer, a food traditionally reserved for nobility. Peasants just got their head chopped off if they hunted deer. But hunts were very big social events for nobility - nobles invited all their friends over. The men could join the hunt, but the big meal afterwards was for the whole family. This would be quite selective - perhaps a few cooks would get killed from scraps, but most peasants would never have eaten deer in their lives.

And just to top it off, Chronic Wasting Disease causes difficulty in movement, and loss of fear of humans. The easiest deer to hunt are those that have it. But it takes a decade or two before the prion disease affects the nobles, so the infection can get quite out of hand.

Answer 13

As you might imagine, there are no diseases that affect a class of people simply because they're members of that class.

Simplifying a lot, disease is environmental or genetic. An example of an environmental disease that would strike a "class" of people would be Black Lung Disease, affecting coal workers, often numbered among the working poor class. (But people don't get it because they're among the working poor, but because they work in the mines....)

I believe what you want will be genetic, but before I go on, let's make something clear. I'm not talking about a genetic disorder. That would be something like autism. That's not a disease. It's not contagious. And you need to think about that, because all diseases are, by definition, contagious.

I therefore assume you want something that's contagious (acting like a real disease) but that's unlikely to be found in the non-noble classes. Not that it isn't impossible, just that it's improbable for some reason that relates to nobility. Ah! That means we're back to environmental. There's something about being noble that makes one more susceptible to this terrifying disease! Let's call it "The Dreaded Gombuu." But before we head over to The Dreaded Gombuu, let's close that discussion about genetics.

You need something that raises the odds of a noble dying from the disease considerably. So much so that people notice! They may even call The Dreaded Gombuu "the nobleman's curse!" In short, you need a disease with a genetic predisposition to the disease. (See also this.)

And you don't necessarily want to explain it. In fact, you don't want to explain it.

I strongly recommend that you not get caught in the trap of explaining the disease or the genetic predisposition. Oh, you might choose a particular disease (e.g., Meningitis) and you may choose how the genetic predisposition came to be (e.g., inbreeding), but if you think about it, people in a roughly medieval world wouldn't understand either one of those things in the first place. What they would be reacting to are symptoms and patterns. And that's what you need to focus on. That's what would make your story cool: the clues are all there, but not the answers.

So, if you want a disease that kills someone quickly, pick one! The only thing that matters is that the symptoms and progression of the disease are good for your story. The top-7 contenders for The Dreaded Gombuu from that link are:

1. Meningitis
2. Flesh eating bug
3. Stroke (not contagious, but has enough environmental factors that the requirement can be ignored — hallelujah for red meat and sugar! Both of which nobles would have access to more than peasants.)
4. Cholera
5. Pneumonic Plague
6. Ebola
7. Dengue haemorrhagic fever

But to be honest, it could be the common cold given the medieval era. A great many diseases we believe are irritating inconveniences were deadly back then due to bad hygiene, nutrition, and low understanding of basic medical practices.

After that, pick how the genetic predisposition to that disease comes to be. The easy one is inbreeding, but it could also be a "genetic defect" from a particular ancestral bloodline (curse the Abrovonavich family from Transylvania!) or truly environmental as it may be a consequence of babies spending tons of time in the presence of something that only the noble would decorate with. I don't know, like asbestos but not as well known. All you need is something that can believably rationalize the genetic predisposition that can be casually mentioned in the course of a story. ("Margaret was well-known for the distinctive Abrovanavich eyebrows....")

And that gives your readers the clues. Clues are good.

Answer 14

Autoimmunity from breast milk

Noble ladies can't be expected to breastfeed their babies - they need to attend court, and wear the most fashionable new outfits, and can't be expected to be at the beck and call of screaming infants. Noble babies have wet nurses.

Breast milk contains antibodies, which help protect the newborn while their own immune system develops. The antibodies work well when the milk-producer and milk-receiver are genetically similar - mother and child. But when the two are unrelated, there is a response not unlike transplant rejection - the noble child develops an inflammatory autoimmune response (a bit like coeliac disease), grows sickly and over time wastes away.

Newborns abandoned in convents often suffer the same fate, depriving religious orders of an important source of new initiates. Not all are affected, though: it was not unusual for poor mothers to deliver in secret and leave the baby with the local monastery, in hope of being hired as a wet nurse for their own child.

Why this has just recently started happening is unclear - probably, the immune response to some mild new pathogen that causes an autoimmune cross-reaction, like Epstein-Barr virus triggering multiple sclerosis.

Although this disease does not affect adults directly, it soon causes despair and panic among the wealthy classes, who find themselves both personally bereaved and genealogically bereft of heirs. Noblemen start taking peasant concubines, who (if they breastfeed their own babies) have much better chances of producing healthy offspring. Noble ladies are incensed and desperate, and not infrequently vindictive - healthy concubine babies often getting poisoned by the official wife, such that it's impossible to discern the link between breastfeeding and health. The church is torn between pressures to stop such sinful behaviour and accusations of divine retribution. Cults arise promising protection from the new Tenth Plague, or declaring the End of Days. Noble families descend into internecine fights between desperate heirs. Marriages, and marriage alliances, break down. The aristocracy is in tatters. Time for a revolution.

Answer 15

Diabetes

Nobles eat noble food. Noble food needs to be well presented, have a superior taste and be expensive! And the foods that have all required components to be noble food are

Pastries

Sugar was very expensive in Medieval times, so they were only accessible to nobles. Therefore peasants were immune to diabetes. This has happened historically, see the history of diabetes.

Answer 16

Make it that the nobility derived from a recent wave of foreign conquerors that took over the region a few centuries ago. Think Indo-Europeans, Greeks, Romans, Polynesians, Bantu, Vikings, ... The greater the difference between the conquerers ancestral environment and their current environment the better. Either environment should have a selective pressure that created a genetic trait like sickle cells. The disease simply exploits this adaptation that is present in one population but not in the other or is mitigated by it.

Maybe the disease is actually malaria. The locals used to inhabit a malaria region and developed a resistance. The climate shifted and malaria left the region. During this time the current nobility conquered the region. To get a stronger effect, have them set up norms against interbreeding. Look at the Indian caste system or the southern United States for inspiration. Now the climate has shifted again, the old disease returns and the nobility is dying in droves.

Answer 17

Make it a mystery, and keep it so. Do not explain anything.

In medieval times, they probably even did not have any means to find out what caused it. All they know is what they saw, and survivors want to ensure it never happens again.

It may even be promoted to some kind of religious belief that shall not be questioned. Some people may see it as a punishment from God, and even if not everyone believed so, fear of [painful] death is enough to motivate anyone. The fear might even be more powerful if no one knows the true reason.

Maybe the peasants were least affected just because they were last to catch it. Who knows. Everyone [in the world of the story] may have their theories, though, and discussions, even fierce debates about the cause may be just as common as feuds over religion.

Anyway, because peasants were those who survived, they just concluded that nobility was a crucial ingredient, and maybe the conclusion was accepted because they hated the noble and blaming them was satisfying. Thus nobility become a thing to avoid, like a taboo. It may even have occurred in the past, cause be long gone, no longer actually capable of affecting anyone, but people are still afraid. Besides, if they found out, they would learn how to avoid it, and nobility would be established again. There may even be a secret society who eg. poison those who gain power, using a rare poison known to only few, making it look like as if it is still going on. They may see themselves as servants of God.

And, maybe the belief spreads like religion. Peasants in the neighboring countries turn against the noble, too, to prevent the same happening to them as well, even though it is in fact unnecessary. Even slightest sign of danger would ignite the "purification". Fear is a strong motivator without any factual cause behind it. The aforementioned secret society may be doing their work.

Answer 18

Organ Specific Parasite
Only the wealthy are allowed to eat the "jewels" of the pig. The parasite that infests the pig "jewels" encysts itself there in a way that survives the brief cooking stage that's used to prepare the delicacy.

The second stage of the parasite's life is to come to maturity in the body of the consumers, lay eggs throughout there body and then die. The maturation process and egg laying lead to massive diarrhea' and thus egg shedding. The castle middens are used to fertilize the fields reserved for the food of the nobility and some of that produce, when semi-rotten ends up in the pig's troughs.

It's a virtuous cycle - parasites feeding on parasites!

Answer 19

There are a number of diet related diseases that attack the wealthy more than the poor. The first one I can think of is gout. This isn't contagious, and it isn't life threatening, but it could give you a starting point. In Asia, poor people were less likely to get beri-beri than wealthier people because they ate brown rice. Brown rice contains more of the vitamin B complex you need, but white rice was considered a delicacy. In Peru, poor people have eaten quinoa for centuries, while wealthier people switched over to rice.

So if you could come up with a contagious disease that is deadly enough for you purposes, where the food eaten by the lower class provices some immunity, You get the result you are looking for.

Incidentally, in England, the black plague created a labor shortage among farm hands that led to the breakdown of the feudal system of farming, and led to hired farm hands taking over. It doesn't have the characteristics you are looking for, but it was a partial factor in the end of feudalism.

Answer 20

In the real world, lead poisoning caused problems for people able to afford piped water.

Maybe in your world, there's a material that's decorative and very expensive like gold, but toxic, and it's used for plumbing fixtures or tableware in the homes of the very wealthy.

Answer 21

Perhaps a combination of two things, both eaten. Please note, I am fabricating this out of real world things, but their interaction is not of our world.

Potatoes are the staple of the peasants. Potatoes are cheap to grow and thus eaten by peasants and are a staple of their diet. The ruling class, nobles and royalty especially, don't eat potatoes, because they are a peasant food. Some of the military and clergy, especially the leadership, have forsaken potatoes as well. Unfortunately, there are a few peasants who also don't eat potatoes, because of a starch intolerance. These few are important.

A new land is discovered, uninhabited. A new spice is discovered, that people call pepper. It's amazing. It's useful. It tastes GREAT! Everyone starts using pepper. There is a long lag (and deadly) sickness caused from ingestion of pepper. You guessed it, in all except those who have the starches. No one realizes they have built up a deadly amount of pepper, until all the royals, nobles, leadership and those few peasants who can't eat potatoes, all die.

Someone, perhaps the hero, who is intelligent, trained, and able, discovers the key linking all who died together. The hero could possible be an apprentice chemist, who figures out the combination. If the story was to be 'realistic' or just a downer, then his girl/sister/wife/whatever is one of those who could not eat potatoes and dies. If it's to be more of a hero saves everyone (important) in the end, then his girl gets sick, and that was causes him to "figure it all out" and save her.

Now, after everyone who was "supposed to die" does, he knows and tells everyone "DON'T ... EAT ... PEPPER!" People stop eating pepper.

This last part is maybe needed, if in your story, those peasants who are elevated to royal status stop eating potatoes, because they are royals, and royals don't eat potatoes. They don't die, because the built up toxin from the peppers has all worn off.

Answer 22

Nobility is all about god-given privilege, social status, noblesee oblige, and most and above all incest. Lots of incest.

Because nobles are so few, the genetic variability among them is quite limited. If they refuse to make children with the masses, then even more so. Over time all kinds of conditions related to genes become commonplace among their lineages.

One example is King Tut, whose parents were siblings. This kind of relationship was not only common but also encouraged for Egyptian nobles. The Wikipedia article on Tut has this passage:

it has been theorised that Tutankhamun had gynecomastia, (...) Wilson–Turner X-linked intellectual disability syndrome, Fröhlich syndrome (adiposogenital dystrophy), Klinefelter syndrome, androgen insensitivity syndrome, aromatase excess syndrome (...).

Now imagine this guy ❤️❤️❤️❤️ing his own sister, which is also his cousin on the 0th degree, and who would have overlapping conditions. The only reason those guys maintained power was because every so often there would be one whose genetic conditions were limited to a combination of madness and ruthlessness.

Answer 23

Ciguatera like disease

An idea taken from the ciguatera.

A particular species, like might be a deer, is considered a delicacy. The places where it lives are turned into hunting reserves and the game ends mostly in the plates of noble people. These things happened often during the middle ages and in many countries the use lasted until the modern age.

One day some merchants coming from a far place by mistake spread the seeds of a plant (or some bacteria) that produces a deadly toxin, but that animal can tolerate it. The toxin accumulates in the tissues and when the animal is eaten it accumulates in the tissues of the people and it takes a while to reach a deadly quantity. When people understand what is the source of the illness is too late.

Answer 24

Peasants are the carriers.

Your disease is endemic within the community of peasants who have already contracted it, thus they have accured natural immunity to the disease. However, these peasants still carry the disease with them and are contagious. (But all of the peasants had immunity which is passed on to their offspring, so they will not get the disease again.) Because the nobility will attempt to minimize interaction with peasants (who they believe are beneath them) they will not catch the disease immediately, but once a member of the nobility spends extended time in the presence of a peasant, he might inhale one of the disease's pathogens. Once one member of the nobility gets this, the entire caste would be succeptible. (Because the disease is not based in a specific thing (animals, liquids, air, etc.) the symptoms and outcomes of the disease are all changeable and malleable.)

Answer 25

Location, Location, Location

There are a lot of answers, but I noted one answer was missing: location.

Often cities were built on hills, with the royalty and nobility living at the highest part of the hill, and peasants towards the outskirts, downhill of the rich and famous. Further, peasants were much more likely to sleep on a simple bed on the floor, while the rich slept on elevated beds. And of course, only the rich could afford a second story house.

Normally, all those work to the advantage of the rich, but in this case, not so much. For whatever reason - gasses from a volcano, swamp gas, fumes from dead animals, natural gas leaking from a fissure - there are toxins in the air that hang like a pall over the city. The toxins are light enough that they don't fill the lower parts of houses, so the peasants sleeping on the floor aren't affected (and they spend most of their day outdoors, where the air is clearer anyway). The rich, sleeping in their high beds, in the most concentrated parts of the gas, die pretty quickly.

This would be very fast. One day, everything is fine; that evening, there's an odd smell in the air, and a few peasants complaining about headaches. By the next morning, anyone sleeping in high beds or on second floors are either dead, or quite sick. A few servants living in their master's house would die, but most of the dead would be the rich. The peasants at the lowest outskirts would be fine, because the gas would pass overhead; the lower income shop owners would mostly be fine, as they wouldn't have fancy beds, but the richest merchants and nobility would not fare so well. The process could take a few days, slowly suffocating the rich, accelerating as they stay in bed.

And after a few still days, the wind picks up and blows the deadly gas away, so there is nothing stopping the peasants from sleeping in the big, fancy beds of the rich.

I realize this isn't a disease as such, but neither the wealthy nor the poor would realize that, and it's effects will be much faster and much more severe compared to diabetes, gout, or even smallpox.

Answer 26

Inherited susceptibility of invading conquerers.

Example: The rulung class of Egypt after Alexander were the Ptolemies. They had no Egyptial ancestry, they were Greek, and they intermarried to preserve their line.

So we can imagine your milieu - maybe the whole planet - is ruled by invaders, who came from somewhere else and interbreed exclusively. So if a nasty plague crops up they would be carrying the genes to make it deadly and the rest of the population just gets a rash. Peasants who are by-blows of the aristocracy, and the odd nobleman whose grandma liked a bit of rough provide a few outliers.

Answer 27

How about modifying an existing disease: Typhus.

Vector: Body lice.

It was a major issue in cold climates that wore a bunch of clothes, it wasn't nearly the issue in warm climates that didn't.

Clothing is a symbol of status, peasants are forbidden to wear it. (They can wear cloaks against the cold, but nothing that conforms to the body.) Typhus does not exist in this land.

The zoonotic jump happens, but this is a version that's considerably more deadly and has a long incubation period. It's the warm season so the peasants are naked. The classes you want to kill have clothes and thus lice and catch it. The ones you want to save are naked, they have few if any lice, they survive.

(And, no, I'm not being unreasonable in postulating a society where peasants do not wear clothes. The idea of indecent exposure is pretty much modern, clothing used to be expensive, for the poor to be working naked was not strange. I'm only taking reality a bit farther in this scenario.)

Answer 28

Diabetes, smoking/expensive drugs, hemophilia, genetic disease due to inbreeding.. they just came out with a story about covid saying that if you get a lot of exercise you will not die from it..