Plausibility check: a deadlier Black Death

For a couple years now, I've been trying to devise a reasonable ATL stemming from a POD in which the Black Death is even deadlier than it is in OTL. (Yes, I know this has been done before, but I didn't know that when I first came up with the idea sometime back in 2007.) My attempts to develop this timeline actually led to my interest in alternate history, so I consider it to be my "baby" of sorts. Unfortunately, history is not my strong suit, so I'm hoping that the kind, more knowledgeable folks on this discussion board could review the basic outline I have for the timeline and check it for plausibility and accuracy. I would be most appreciative of any input.

The overarching theme for my proposed ATL is: What would the world be like if the Black Death wiped out most of the population of Europe? My intended POD is during the year 1347, when a new mutation spreads throughout the Yersinia pestis population which is on its way to infiltrate southern Europe. The mutation increases the prevalence of the pneumonic and septicemic forms of the plague compared to that of the bubonic form. This enhances the communicability and virulence of the disease by roughly threefold, resulting in the extermination of about 90-95% of the population of Europe.

With Europe almost wholly depopulated, the Ottoman Turks, the Mamluk Arabs, and the Timurids vie for control of the subcontinent, with the Turks eventually prevailing and taking control of almost all of Europe. Islam becomes the dominant religion of the West, as the Catholic Church collapses in the wake of the plague. Christianity exists only in a small minority of the European population from then on. The Renaissance and (later) the Industrial Revolution still take place, although they are focused primarily in the Middle East and China and delayed by about 50-100 years.

Overseas colonization is also set back without the exploits of European conquistadors. This delays the "discovery" of the New World by the Old, giving the Mexicans (Aztecs) and Inkas time to consolidate their hold on the American continents. The Mexicans serve as the progressive catalysts for the indigenous American population. As their influence spreads northward, Mexican-style farming and city-building becomes popular throughout much of North America. City living increases disease resistance, mitigating the impact of foreign germs brought by explorers from the Old World.

The Chinese make contact with the Americas via the Pacific in the late 1500s or early 1600s, around the same time that the Arabs and Turks do the same on the Atlantic side. The Mexicans adopt Old World technology (including metalworking and firearms), allowing them and their North American allies to better defend themselves from Chinese and Muslim would-be colonists. The Mexican Empire (capital: Tenochtitlan) owns Central America and southern North America, and the Caribbean Sea is a Mexican lake. The Inka Empire (capital: Qusqu), though rivals with the Mexicans, adopt their strategy and end up controlling almost the entire South American continent. The Chinese, Turks, and Arabs do establish coastal colonies in the New World, but do not penetrate inland as far as in OTL.

China winds up dominating eastern and southeastern Asia, Siberia, and the Pacific, resulting in an empire larger than even that of the Mongols. In eastern Asia, only the Japanese (capital: Kyoto) manage to avoid conquest by the Chinese, despite numerous attempted invasions. A long, drawn-out civil war in the 1900s between China and rebellious Tibetan guerrillas results in the eventual defeat of the Tibetans. During the 19th and 20th centuries, China starts to become more liberal and democratic, leading to the formation of the Republic of China and the independence of several colonies in southeast Asia and Australia. The majority of Chinese are of the peaceful Buddhist faith (although, as in Turkey, progressive liberal reforms steadily increase the prevalence of secularism), but China is beset with racism toward its non-Han citizens.

Democratization also occurs in Turkey, which has rivaled the Chinese for centuries in terms of economic and military power. By the 21st century, the Turkish Sultanate (capital: Istanbul) holds Anatolia and almost all of Europe from the Atlantic to the Urals, the Arab Sultanate (capital: Cairo) controls the Arabian Peninsula and northern Africa, the Iranian Empire (capital: Samarqand; descendant of the Timurid Empire) controls much of southern and central Asia, the mainly Hindu Bharat Republic (capital: Madurai; descendant of the Vijayanagara Empire) holds southern India, the Kingdom of Delhi (capital: Delhi) has northern India, and the Republic of China covers OTL China, Siberia, Alaska, Korea, Taiwan, parts of southeast Asia, and most of the Pacific. Sub-Saharan Africa is largely peaceful and is dominated by four major nations: the Ethiopian Empire, the Songhai Empire, the Kingdom of Kongo, and the Kingdom of Zimbabwe.

A devastating attack in Istanbul by fundamentalist Christian terrorists in the early 21st century results in a severe, worldwide economic depression. In the wake of the depression, revolutionaries take over the corrupt Arab Sultanate, establishing the Arab Caliphate, an authoritarian Sunni socialist state. With the sultan dead and former caliph forced to abdicate, the rebel leader would combine the positions and appoint himself the new caliph. In the Iranian Empire, the response to the crisis is less violent. Discontent is spreading due to the depression and over the controversial new Cairo caliph. A dissident Shia nationalist organization led by a charismatic man claiming to be an Imam would soon take control of Iran, setting up an dictatorship to supplant the old Sunni regime and declaring the Cairo caliph illegitimate. The Turkish Sultanate, though primarily Sunni, grows increasingly secular, in part due to continual scientific and social progress and in part because many Turks are disillusioned by the parody of a valid religious leader in Cairo.

The Turks and Arabs have historically been bitter enemies, competing for control of the Middle East and Mediterranean in numerous wars over the centuries. By the early to mid-21st century, though, their animosity for each other would wane as a common enemy emerges in Iran. The Imam rants to the Iranian public about the blasphemous Sunni socialists and Turkish secularists. He also directs his wrath toward the Hindus of India, who the Muslims of southern Asia have long tried to subjugate. The Imam's intense prejudice toward Hinduism and Hindus as a people becomes apparent, forcing many so-called "heathens" to flee Iran to escape persecution. He blames the industrious Hindus for causing the depression. In the 2030s, Iran would anger the Turks and Arabs by forcibly annexing the western coast of the Kingdom of Delhi, along the Arabian Sea. When, shortly afterward, the Iranian army uses this new territory to invade Bharat, the Turks and Arabs, allies of Bharat, declare war on Iran.

The Mexican Empire, allied with Iran, attacks and captures the Chinese colony of Hawaii, initiating a separate war over control of the Pacific. Less progressive than their northern neighbors, the strength of the Inka Empire has deteriorated over the years, allowing the Mexican army to spread southward and claim the northern part of the Inka Empire as the puppet state of South Mexico. The North Mexican Confederation, composed of many allied North American indigenous tribes, is displeased at Mexico's imperialistic attitude but does not wish to anger its strongest ally. Thus, the NMC remains adamantly neutral in the war. A long global conflict ensues, drenching the world in blood.

So what does everybody think? I'm especially concerned about the plausibility of how the plague became more deadly and how the native Americans could have successfully warded off Old World invaders. Thanks in advance for your help.

EDIT: I should note that even though it's the early 21st century, the belligerent nations are going into the war with technology roughly equivalent to that of WWI in OTL. They are about a century behind us. And in case I couldn't make it more obvious, the war is (for the most part) analogous to WWII.
 
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With Europe almost wholly depopulated, the Ottoman Turks, the Mamluk Arabs, and the Timurids vie for control of the subcontinent, with the Turks eventually prevailing and taking control of almost all of Europe. Islam becomes the dominant religion of the West, as the Catholic Church collapses in the wake of the plague. Christianity exists only in a small minority of the European population from then on. The Renaissance and (later) the Industrial Revolution still take place, although they are focused primarily in the Middle East and China and delayed by about 50-100 years.
Err... Say what?

The Black Death was hardly just a European phenomenon. The Turks were hit OTL, no? and I would expect the Mongols to have been, too.

The Chinese may not have been, one would need to check that, but if the new bug is around, they'll get it sooner or later.

If you want to say it hits Europe harder, or something, you could make a modified version work...
 
and I would expect the Mongols to have been, too.
Just off the top of my head, I think the western Mongols/Golden Horde began to experience serious problems besieging anybody around that time, as their armies would inevitably fall victim to plague of some kind or another.

'Sides, the whole thing started along the Silk Road anyways. If some Mongols and Turks didn't catch the plague, I'll be a monkey's uncle.
 
Err... Say what?

The Black Death was hardly just a European phenomenon. The Turks were hit OTL, no? and I would expect the Mongols to have been, too.

The Chinese may not have been, one would need to check that, but if the new bug is around, they'll get it sooner or later.

If you want to say it hits Europe harder, or something, you could make a modified version work...

Yes, I know the Black Death hit all over Eurasia and North Africa. AFAIK, it started in the 1330s in east central Asia, and spread to China, India, and the Middle East. The Mongols transported it westward along the Silk Road, eventually transferring it to Genoan sailors on the Crimea, who then brought the disease into southern Europe. It spread northward and curved back eastward, finally ending in western Russia in the early 1350s.

In the ATL, a mutation in the plague population just beginning to spread into southern Europe makes the disease almost three times deadlier (exactly how I'm uncertain, but I'm trying not to gloss over details). So the Black Death does as much damage to the rest of the Old World (killing approximately 1/3 of population of the areas it hit) in the ATL as in OTL. Europe is at the end of the line, and that's when the disease goes into overdrive, wiping out almost all Europeans.

I'm also aware that there are theories that the Black Death was not caused by the bubonic plague bacterium Yersinia pestis. However, I'm going with the majority opinion on this.
 
Just off the top of my head, I think the western Mongols/Golden Horde began to experience serious problems besieging anybody around that time, as their armies would inevitably fall victim to plague of some kind or another.

'Sides, the whole thing started along the Silk Road anyways. If some Mongols and Turks didn't catch the plague, I'll be a monkey's uncle.

You're right about the Mongols. In OTL, the Black Death devastated the Golden Horde, and they never recovered from it.

The Turks caught it too, but no worse than anywhere else (both in OTL and the ATL).
 
OK, next question. In Europe, the Black Death (whatever it was), came in several waves, and then vanished. Did it resurge from reservoirs in Europe, or was it reintroduced each time? It'd have to be the former, I'd think, if the virulent form was to be and stay European. Hmm... OK, that might work

Also, if the virulent mutation happens as it hits southern Europe, how does it not flow back to the Ottomans, say. Oh. because it's immunologically close enough that their previous exposure to the mild form protects them. OK, I'll buy that.
 
OK, next question. In Europe, the Black Death (whatever it was), came in several waves, and then vanished. Did it resurge from reservoirs in Europe, or was it reintroduced each time? It'd have to be the former, I'd think, if the virulent form was to be and stay European. Hmm... OK, that might work

By several waves, are you talking about the Justinian plague and the various other outbreaks which have occurred throughout history? I'm not sure where the other outbreaks originated, but some might have come from the same reservoir of flea-bitten rodents in Central Asia that caused the Black Death. There may also be reservoirs elsewhere, but I don't know for certain.

Also, if the virulent mutation happens as it hits southern Europe, how does it not flow back to the Ottomans, say. Oh. because it's immunologically close enough that their previous exposure to the mild form protects them. OK, I'll buy that.

You seem to be answering your own questions. :D
Yes, that was my thought, that the original strain of the plague provides immunity to the stronger strain. I think that makes sense, anyway.
 
By several waves, are you talking about the Justinian plague and the various other outbreaks which have occurred throughout history? I'm not sure where the other outbreaks originated, but some might have come from the same reservoir of flea-bitten rodents in Central Asia that caused the Black Death. There may also be reservoirs elsewhere, but I don't know for certain.
Nope, I'm talking about recurring waves, see below
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2630035/ said:
The second pandemic originated in India, China, or the steppes of Russia, touched the shores of western Europe (Messina) in the autumn of 1347, circumnavigated most of continental Europe in less than three years and eventually struck places as remote as Greenland. While the first lasted just over two centuries and the third a mere twenty-five years in pandemic form, this second wave returned periodically for nearly five hundred years in western Europe. Its last attack in Italy was at Noja (Noicattaro), near Bari, in 1815,3 but it persisted longer in eastern Europe and Russia. Its cycles, however, lengthened from a hit about every ten years for any locale during the latter half of the fourteenth century to absences of 120 years or more for major cities at least in Italy by the seventeenth century. Despite repeated claims in textbooks, the plague of Marseilles in 1720–1 was not this pandemic's European finale.4 In 1743, 48,000 perished from plague in Messina; in 1770–1 over 100,000 in Moscow; and in the Balkans, Egypt, Asia Minor and Russia this Black-Death-type of contagious plague may have persisted as late as 1879.5
 
Nope, I'm talking about recurring waves, see below

Hmm, I don't know about those. My research into the plague stopped with the Black Death itself, which ended in the 1350s. I haven't read the article through yet, but it's possible that a reservoir of plague rats was established in Europe.
 
I don't know anything about the black death, but what happens to the Jews, they were persecuted because they were slightly more immune because they bathed. just asking, otherwise i'd love to see the TL. FYI there was a short story written in the '80s (i'll get more details in you want just message me) along similar lines with the Ottomans taking over all of Europe, might be worth looking up
 
That is an improbably high death rate. Even in the virgin fields of the America's the death rates from from multiple new diseases didn't quite reach that percentage.
 
I don't know anything about the black death, but what happens to the Jews, they were persecuted because they were slightly more immune because they bathed. just asking, otherwise i'd love to see the TL. FYI there was a short story written in the '80s (i'll get more details in you want just message me) along similar lines with the Ottomans taking over all of Europe, might be worth looking up

The Jews didn't fare too well in the ATL either. The few European Jews who survived the plague were persecuted by the few but more numerous Christians who survived as well. (I actually didn't know about the bathing thing -- that's very interesting.) The Muslims who invaded Europe afterward weren't too friendly to the Jews either. Thus, as in OTL, there was a Jewish diaspora throughout Europe as the poor Jews sought refuge from persecution. It's not all bad for them, though. Some Jews establish a successful colony in North America free from violent anti-Semites. They adopt this as their new homeland, and many Jews emigrate to the safety of the colony.

There are three AH books published that I know of which involve a deadlier Black Death, but they are all from the 2000s. The Years of Rice and Salt by Robinson, The Gate of Worlds by Silverberg, and In High Places by Turtledove. I read the last two, and I started the first one, but I only got about 20% through before I gave up and just read a summary of it. I couldn't stand all that crap about the bardo.
 
That is an improbably high death rate. Even in the virgin fields of the America's the death rates from from multiple new diseases didn't quite reach that percentage.

Really? Do you know what the average rate was in the Americas? I definitely don't want to go beyond the bounds of believability.
 

Maur

Banned
This enhances the communicability and virulence of the disease by roughly threefold, resulting in the extermination of about 90-95% of the population of Europe.
This is very, very bad. ;)
(I guess we handwave the obvious biological difficulties associated with that)
With Europe almost wholly depopulated, the Ottoman Turks, the Mamluk Arabs, and the Timurids vie for control of the subcontinent
Why wouldn't Middle East and North Africa also be hit by plague?

EDIT/ Ah, a mutation just in time when it appears in Europe? And i assume that resistance already posessed still works? Well, ok then, although IIRC, Maghreb gets hit too.

The Renaissance and (later) the Industrial Revolution still take place, although they are focused primarily in the Middle East and China and delayed by about 50-100 years.
That's rather unlikely, isn't it? Why would it take place?

This delays the "discovery" of the New World by the Old, giving the Mexicans (Aztecs) and Inkas time to consolidate their hold on the American continents.
If you delay the discovery by a century only, you still have New World civilizations at basically 2000 BCE level of Old World development.

City living increases disease resistance, mitigating the impact of foreign germs brought by explorers from the Old World.
It's a misconception... it won't increase resistance to OW diseases. Since they aren't present in NW, so they aren't there to promote resistance in population. What would happen would be indigenous NW diseases that hit OW in turn, too.

The Chinese make contact with the Americas via the Pacific in the late 1500s or early 1600s, around the same time that the Arabs and Turks do the same on the Atlantic side.
Why would Chinese do that early? Or Turks and Arabs?

I'll leave the rest since the premise has few problems so there is not much point...
 

Maur

Banned
Really? Do you know what the average rate was in the Americas? I definitely don't want to go beyond the bounds of believability.
Well, it's theoretically possible... but i'm not sure if it's believable.

Hmm. You might want to invent a disease that's endemic to temperate zone similar to our usual tropical ones. Although that's rather unprobable too.
 
Err... Say what?

The Black Death was hardly just a European phenomenon. The Turks were hit OTL, no? and I would expect the Mongols to have been, too.

The Chinese may not have been, one would need to check that, but if the new bug is around, they'll get it sooner or later.

If you want to say it hits Europe harder, or something, you could make a modified version work...

The Chinese had a higher percentage death rate from their outbreaks of the Black Plague than Europe (suspected due to higher population densities and less patchiness of population).

95% death rate is stupid as well (no disease has ever reached that level - the Native American die offs got there via multiple diseases hitting in concert), but if you have that in Europe you'll be seeing +80% death rates in the middle east and >95% death rates in the densely populated bits of Asia. Eurasia is really one epidemiological unit after all...

Also immune response to Bubonic versions of Yersinia pestis give minimal advantage against Pneumonic infection.
 
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The problem is that Yersinia pestis lives in broad range of rodents. Thus even if such a deadly plague would develope and if it wouldn't spread, it would still remain in Europe, killing of any would be colonists.

Also immune response to Bubonic versions of Yersinia pestis give minimal advantage against Pneumonic infection.

This is not correct, a survived bubonic plague gives resistance against all formes of plague, it is just that the vaccine against bubonic plague doesn't work against pneumonic plague.
 
95% death rate is stupid as well (no disease has ever reached that level - the Native American die offs got there via multiple diseases hitting in concert),

could we do that in Europe too? Along with the plague, have outbreaks of smallpox, pneumonia, whatever? Instead of one disease getting meaner, what about a variety of diseases striking all at once?
 
NOTE: Rather than using multi-quote, I've combined the last few responses together. In italics are previous quotes, in bold italics are the responses to the previous quotes, and in regular font is my response.

~~~~~

DJC:
This enhances the communicability and virulence of the disease by roughly threefold, resulting in the extermination of about 90-95% of the population of Europe.

Maur:
This is very, very bad.
(I guess we handwave the obvious biological difficulties associated with that)

No, I don't want to handwave. I have a Bachelor's in biology and I respect the field greatly (as well as science in general), so I'm trying to provide a plausible biological explanation for the deadlier form of the plague. However, I don't know much about epidemiology, leaving me at a disadvantage when it comes to things that are obvious to more knowledgeable folks in the field.

~~~~~

DJC:
With Europe almost wholly depopulated, the Ottoman Turks, the Mamluk Arabs, and the Timurids vie for control of the subcontinent

Maur:
Why wouldn't Middle East and North Africa also be hit by plague?

EDIT/ Ah, a mutation just in time when it appears in Europe? And i assume that resistance already posessed still works? Well, ok then, although IIRC, Maghreb gets hit too.

According to the maps I've seen, the path of the plague splits, with one wave spreading from the Middle East into northeast Africa and another wave moving into southern Europe and northwestern Africa. It is this latter wave that experiences the mutation. So the Berbers in the Morocco area get hit by the deadlier plague as well as Europe.

~~~~~

DJC:
The Renaissance and (later) the Industrial Revolution still take place, although they are focused primarily in the Middle East and China and delayed by about 50-100 years.

Maur:
That's rather unlikely, isn't it? Why would it take place?

Well, as far as I know, the Middle East was quite advanced in scientific knowledge, perhaps comparable to Europe. In OTL, the Europeans reached the Renaissance and Industrial Revolution stages first, but in their virtual absence, I would expect the Middle East to reach those stages first instead (although a bit later). I'm no expert on Chinese history, but I thought they were pretty advanced in scientific knowledge too, if not so much as the Europeans and Middle Easterners. So I was anticipating that they wouldn't be too far behind the Middle East in technological progress. Of course, I may be totally off the mark here, so anyone should feel free to correct me.

~~~~~

DJC:
This delays the "discovery" of the New World by the Old, giving the Mexicans (Aztecs) and Inkas time to consolidate their hold on the American continents.

Maur:
If you delay the discovery by a century only, you still have New World civilizations at basically 2000 BCE level of Old World development.

Yes, I knew that accelerating the progress of the New World civilizations was one of the potentially weakest part of my premise. I was hoping that the century-long delay would give the Mexicans and Inkas enough time. Perhaps in the ATL, there could be a brief, early contact (prior to the major attempts at colonization) between the Mexicans (or Inkas) and the Old World which would provide the native Americans with Old World tech (mainly metalworking and firearms). Even if they adopted Old World tech and began to use it widely, I know it wouldn't put the native Americans nearly on par with the Old World, but I was hoping it could give them enough of an edge to ward off being wholly conquered as in OTL. Is this still unrealistic?

Ideally, I'd like the Mexicans to remain in power until at least the 21st century, and if possible, the Inkas and native North Americans too. But if there's no way this can realistically be done, I'll have to modify the story. I still hope there a way to keep at least Mexico going, even with reduced territory.

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DJC:
City living increases disease resistance, mitigating the impact of foreign germs brought by explorers from the Old World.

Maur:
It's a misconception... it won't increase resistance to OW diseases. Since they aren't present in NW, so they aren't there to promote resistance in population. What would happen would be indigenous NW diseases that hit OW in turn, too.

You know, I've wondered why the Old World diseases did so much damage to the New World, while NW bugs didn't do nearly as much damage to the OW. So, as I understand it, urbanization promotes disease transmission and in turn disease resistance, but only to those specific diseases, which obviously would differ between the OW and NW. If the NW did become more urbanized in the extra century they get before OW colonization, would there be more NW diseases and more damage done to the OW in the ATL? In this case, both sides would suffer, the OW more so than in OTL. Would the NW still suffer as much as in OTL though? Perhaps the NW fares relatively better than in OTL (since the OW is hit harder), giving the NW a better chance to stave off invasion.

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DJC:
The Chinese make contact with the Americas via the Pacific in the late 1500s or early 1600s, around the same time that the Arabs and Turks do the same on the Atlantic side.

Maur:
Why would Chinese do that early? Or Turks and Arabs?

When you say early, are you comparing the Chinese, Turks, and Arabs to the Europeans in OTL? In the ATL, they reach the OW a century later than the Europeans do in OTL. Would a later date of contact for either the Chinese or Turks/Arabs be more realistic?

~~~~~

Maur:
I'll leave the rest since the premise has few problems so there is not much point...

Well, if you see any other problems, even if they are minor, I'd appreciate hearing about them. Thanks a lot for your feedback on this.

~~~~~

DJC:
Really? Do you know what the average rate was in the Americas? I definitely don't want to go beyond the bounds of believability.

Maur:
Well, it's theoretically possible... but i'm not sure if it's believable.

Hmm. You might want to invent a disease that's endemic to temperate zone similar to our usual tropical ones. Although that's rather unprobable too.

"Believable" was perhaps the wrong word -- I'm looking for realistic. I don't at all want this to go ASB. I'd rather not invent any disease if I don't have to.

~~~~~

DJC:
With Europe almost wholly depopulated, the Ottoman Turks, the Mamluk Arabs, and the Timurids vie for control of the subcontinent, with the Turks eventually prevailing and taking control of almost all of Europe. Islam becomes the dominant religion of the West, as the Catholic Church collapses in the wake of the plague. Christianity exists only in a small minority of the European population from then on. The Renaissance and (later) the Industrial Revolution still take place, although they are focused primarily in the Middle East and China and delayed by about 50-100 years.

Dathi THorfinnsson:
Err... Say what?

The Black Death was hardly just a European phenomenon. The Turks were hit OTL, no? and I would expect the Mongols to have been, too.

The Chinese may not have been, one would need to check that, but if the new bug is around, they'll get it sooner or later.

If you want to say it hits Europe harder, or something, you could make a modified version work...

Nugax:
The Chinese had a higher percentage death rate from their outbreaks of the Black Plague than Europe (suspected due to higher population densities and less patchiness of population).

95% death rate is stupid as well (no disease has ever reached that level - the Native American die offs got there via multiple diseases hitting in concert), but if you have that in Europe you'll be seeing +80% death rates in the middle east and >95% death rates in the densely populated bits of Asia. Eurasia is really one epidemiological unit after all...

Also immune response to Bubonic versions of Yersinia pestis give minimal advantage against Pneumonic infection.

I wasn't sure about how hard the Chinese were hit. There's a whole lot out there in the literature about the effects of the Black Death in Europe, but not so much on other areas of the world. I don't recall where, but I saw an estimate of around a 1/3 mortality rate in China. Even if the Chinese were hit harder in OTL than the Europeans in OTL, did the Chinese lose anywhere close to 80% or more of their population? If not, then the deadlier plague in the ATL would still do the Europeans more relative damage than the original strain which hits China both in OTL and the ATL.

However, are you saying that the deadlier strain of the plague would spread from Europe back into all the places where the original strain hit? I had the mutation increase the prevalence of the pneumonic form of the plague because I thought it would help the disease spread through Europe faster and because it has a higher mortality rate than the bubonic form. Although, now that I think about it, the plague spread pretty damn fast across Europe in OTL anyway, so maybe speed isn't an issue. And I didn't know about the lack of resistance between the two forms of the plague. I had assumed there would be some resistance because it's the same species of bacterium. Why doesn't this happen?

A third form, septicemic plague, was I believe nearly as deadly as the pneumonic form. Perhaps the mutation could increase the prevalence of this form of the plague? Or maybe simply a more potent version of the bubonic form? What do you think would be most realistic? If Eurasia is one epidemiological unit, would this mean the deadlier form of the plague would simply head back across the continent to China again? This would level the Old World evenly and kill my premise, but I don't want to go ahead with something if it's unrealistic.

~~~~~

Nugax:
Also immune response to Bubonic versions of Yersinia pestis give minimal advantage against Pneumonic infection.

Kalan:
This is not correct, a survived bubonic plague gives resistance against all formes of plague, it is just that the vaccine against bubonic plague doesn't work against pneumonic plague.

Uh oh. I have conflicting advice. So if one gets resistance regardless of the form of the plague, then the deadlier strain wouldn't be able to continue on outside of Europe, where the original strain already swept through, right?

~~~~~

Kalan:
The problem is that Yersinia pestis lives in broad range of rodents. Thus even if such a deadly plague would develope and if it wouldn't spread, it would still remain in Europe, killing of any would be colonists.

The colonists were already hit with and survived the original form of the plague, so wouldn't they still have resistance? I know that the plague recurred in Europe numerous times after the Black Death, although without doing nearly as much damage. I don't know how it kept recurring though. Was it being re-transmitted by a reservoir of rodents either in or outside of Europe? I suppose it was able to recur because each outbreak was different enough from the previous outbreak so that any prior resistance would be useless. Does this make sense?

~~~~~

Nugax:
95% death rate is stupid as well (no disease has ever reached that level - the Native American die offs got there via multiple diseases hitting in concert),

Dave Howery:
could we do that in Europe too? Along with the plague, have outbreaks of smallpox, pneumonia, whatever? Instead of one disease getting meaner, what about a variety of diseases striking all at once?

More diseases are possible, but this includes multiple PODs, where I want to just have one.
 
95% death rate is stupid as well (no disease has ever reached that level - the Native American die offs got there via multiple diseases hitting in concert), but if you have that in Europe you'll be seeing +80% death rates in the middle east and >95% death rates in the densely populated bits of Asia. Eurasia is really one epidemiological unit after all...

If you are talking die-offs in inhabited areas, you are probably right, as a disease that virulent would probably burn out before it got very far, and/or you have peasants stoning any foreigner, keeping sick visitors out.

For fatality rates, Rabies is 100% (I don't believe anyone has ever survived it without the vaccine). The nastiest Ebola is 'only' 90% fatal, apparently. I thought it was higher.

In a MODERN society, an 80%+ death rate might end up being higher, as we are so dependent on our infrastructure, and millions of dead, rotting bodies won't help. In a peasant society, if 2 peasants survive in an area with 200 people, they're rich (if all the livestock didn't die too).
 
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