AHC: Latest possible Black-Death-like pandemic

What is the latest possible date a disease could be as, or more, severe, than the Black Death?

I put this in Before 1900 because I wasn't sure if such a pandemic could happen in the more advanced 20th century; however, if the Spanish influenza could get a lot worse, to Black Death levels worldwide, that would satisfy the challenge.
 
If you mean by death rate (and confining this to history) this morning. Of course it could also happen later today.

If you mean in terms of the social impact it had in Europe, I would guess the first one to strike post-1100 would be the only one to have such an effect. In other words, there can't be another Elvis because after Elvis, everyone understood what that meant. Similarly, there were many lethal pandemics after the Black Death, and with a little less luck there could have been similarly lethal ones well into the twentieth century. But people understood what a black death was, which means it would not shatter their world view in the way the first one (allegedly) did. I suspect it will take us at least another century of hard work and lucky escapes to develop such a mindset.
 
Wasn't the spanish flu, while a different illlness, not that far? It screwed a world screwed already by war...

While the total fatality figures of the spanish flu were at least equal, if not higher than the ones of the black death in the mid 14th century, the relative figures were substantially lower due to a much bigger global population. The advantage for the black death was, that nobody up until the 19th century had the faintest idea what was the real cause for contagious diseases and thus about any suitable counter measures.
 
But one detail also that is worse for Spanish Flu than Black Death - the spanish flu killed due to an imunity screw up MORE healthy, young peoples than weak ones, apparently...
 
I recently read "Biology of Plagues: Evidence from Historical Populations" by Susan Scott and Christopher Duncan (2001), which makes a fairly compelling case that the Black Death was NOT caused by Yersinia pestis, as was concluded in the late 19th century, but was in fact a viral disease, most likely related to the Ebola Fever family. Their evidence is diverse, but the most suggestive to me is the fact that modern Bubonic Plague has a mere 2%-4% mortality rate, compared to the far higher mortality rates (50%-90%) reported for the Black Death, and the fact that Ebola-like diseases actually fit the described symptoms and epidemiology better than Bubonic Plague does (leaving aside the vast difference in mortality rates). Actually, the epidemiology evidence conclusively excludes Yersinia pestis as the cause for the Black Death, the required timing simply does not work out, whereas a filovirus such as Ebola fits the reported timing perfectly.
 
Lets say there's a disease like the Black Death, but twice as dangerous, and it pops up long after the original Black Death. Would it be possible to catapult the world back into a Dark Age? Yes, I know that the OTL Dark Age was only European and that it's supposed to not have been as dark as is commonly said.
 
Their evidence is diverse, but the most suggestive to me is the fact that modern Bubonic Plague has a mere 2%-4% mortality rate, compared to the far higher mortality rates (50%-90%) reported for the Black Death, and the fact that Ebola-like diseases actually fit the described symptoms and epidemiology better than Bubonic Plague does (leaving aside the vast difference in mortality rates).

There's a few problems with this theory. First of all, bacterial diseases evolve to be less lethal over time-take the case of syphillis. When a lethal strain broke out in early modern Europe, it evolved in a very short time into a much less lethal disease that took much longer to kill its victims. In addition, if an ebola-like disease actually managed to evolve to spread from human to human as easily as the Black Death seemed to, why didn't it become endemic in the areas it hit? Sure, it could have taken a few centuries, but if measles or smallpox could do it why not black death?

Finally, be wary of claims regarding ancient diseases and populations. Population sizes and changes can be much more controversial than any individual historian will let on. And as the agent of the Black Death conveniently did not leave any physical remains, there is nothing for anyone to study. Any claims about the agent are, at best, informed speculation.
 
Lets say there's a disease like the Black Death, but twice as dangerous, and it pops up long after the original Black Death. Would it be possible to catapult the world back into a Dark Age? Yes, I know that the OTL Dark Age was only European and that it's supposed to not have been as dark as is commonly said.

Probably not, because of writing. Although it would delay development, as soon as any society stabilized in the wake of the disease they would crack open some books written by their ancestors and get back to developing science, mathematics and engineering as they did before. That said, a massive drop in population could certainly delay or even prevent the industrial revolution, and there would be a time where affected societies would be severely de-stabilized. If that de-stabilization gets out of hand, civil strife could keep some parts of the world in the dark ages.
 
Lets say there's a disease like the Black Death, but twice as dangerous, and it pops up long after the original Black Death. Would it be possible to catapult the world back into a Dark Age? Yes, I know that the OTL Dark Age was only European and that it's supposed to not have been as dark as is commonly said.

You would need for the disease to stick around to get an effect like that. Your primary problem is that the knowledge base is very well established and distributed. Unless you create a near-permanent reason not to have urban settlements, you will have cities and trade connections come back very soon.
 
Probably not, because of writing. Although it would delay development, as soon as any society stabilized in the wake of the disease they would crack open some books written by their ancestors and get back to developing science, mathematics and engineering as they did before. That said, a massive drop in population could certainly delay or even prevent the industrial revolution, and there would be a time where affected societies would be severely de-stabilized. If that de-stabilization gets out of hand, civil strife could keep some parts of the world in the dark ages.

The more significant the drop in population, the bigger the incentive to invent labour-saving devices. That holds true several times in history. Water propelled mills were first used on a larger scale in the Roman Empire in the late 2nd century, after the Antonine plague, the renaissance startet only a few decades after the Great Plague of the mid 14th century and the industrial revolution a few decades after the plague of the 1660s.

Another important factor in the wake of large pandemics is that, as cruel as it may sound, they improve the quality of the gene pool of the surviving population. It's pretty simple darwinistic logic, the weak perish, the fittest survive. This is also one of the reasons why following waves of plague had a significantly lower fatality rate. The survivors of the first wave were either immune from the very beginning or had developped an immunity while overcoming the infection.

It is interesting, that the modern populations of areas, that were hit most hard by the Great Plague and other epidemics in the past, have a better immunity against any kind of contageous diseases, they are even less likely to succumb to an HIV infection than someone from a population of an area, that was hit less hard or even completely spared by epidemics in the past.
 
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