why were there no new world diseases?

The native americans died in huge numbers after the Europeans came to the new world due to the fact that they were not immune to many of the diseases that the europeans had. So, why were the europeans not affected by diseases of the new world? And what would have happened if such a thing happened?
 
Syphilis originated in the New World and was responsible for around five million deaths when it initially came to Europe. It remained a devastating disease until the invention of penicillin, with epidemics being frequent.
 
I think you meant for this to be in the pre-1900 forum.

To the question, part of it is zoonosis, or rather lack thereof. There are dramatically less animals living in close proximity to humans in the Americas as a result of far fewer domestic animals, but some of major domestic animals in the Americas (Llamas and Alpacas) are also just less disease prone in general, which means you're unlikely to get diseases jumping species in such a scenario. The other issue of course is one of population density, diseases need a large population to exist in so they can survive and thrive, and this goes doubly for zoonotic diseases. COVID is a good example, it started in an area populated densely by both humans and animals which allowed the disease to jump from host to host and species to species in a short enough time span to not die out and it was able to adapt and evolve. In most of the pre-Columbian Americas, that population density just isn't there.
 
I think you meant for this to be in the pre-1900 forum.

To the question, part of it is zoonosis, or rather lack thereof. There are dramatically less animals living in close proximity to humans in the Americas as a result of far fewer domestic animals, but some of major domestic animals in the Americas (Llamas and Alpacas) are also just less disease prone in general, which means you're unlikely to get diseases jumping species in such a scenario. The other issue of course is one of population density, diseases need a large population to exist in so they can survive and thrive, and this goes doubly for zoonotic diseases. COVID is a good example, it started in an area populated densely by both humans and animals which allowed the disease to jump from host to host and species to species in a short enough time span to not die out and it was able to adapt and evolve. In most of the pre-Columbian Americas, that population density just isn't there.
oh sorry about the wrong forum, can someone change this? @CalBear i think?. So, you are saying that, due to less population density and the type of animals, there were no major diseases here. Thats interesting
 
Nailed it. The New World's relative lack of domesticable plants and animals compared to the Africa/Eurasia group was a serious hindrance to population growth and the parallel growth of diseases communicable between farm animals and humans.
This is also why any thread postulating a smaller disparity between the Old and New Worlds by 1490+ is almost guaranteed to be tossed to the ASB forum since it requires a change to the flora and fauna of either/both continents, not human agency.
 
Another aspect is that Europeans lived for thousands of years in situations were there was a lot of travel and movement of animals and humans between a larger area (Europe, Asia and Africa) This promotes disease spread but also general resistance to a wider array of diseases. Populations in the Americas obviously travelled and mingled to an extent within each other but were still as pointed out low density and isolated from the rest of the world. (also what's true for humans/host is also true for diseases themselves)

There's another factor as well, New world diseases did kill Europeans when they got there but because they had travelled there to catch them that meant a couple of points regarding wiping out larger populations of Europeans

1). So long as the disease wasn't brought back to the Old world (via at best a several weeks long sea journey) the core population wasn't hit. Syphilis is still being debated as being a New world disease that jumped the Atlantic or not, and that did kill a lot of people, but its pathology meant it was never going to be a Black death in terms of ripping through a population and killing large percentages quickly.

2). there was always more Europeans coming across to replace any lost I.e that European population was always being topped up by a source outside the infection zone.

The opposite was true for american native population in terms of America vs European diseases, the introduced diseases quickly reached their entire population and there was quickly no reservoir of population outside the infection zone. And while movement within the larger populations tended to be less there wasn't an oceanic barrier to protect them and act as quarantine.

3). in terms of human to human infection you need lots of interactions between both populations to maximise cross infection, but a lot of native populations in the Americas were being reduced by European diseases, and a lot of that happened by European diseases travelling in the native population ahead of newly refreshing European population having initially been introduced from the first Europeans and then transmitted by Native populations. I.e I as a native American can't give the new European settlers appearing for the first time in my area my nasty disease (even if I had one) if I and the vast majority of my local community died from European diseases that got to us 50 years earlier without us ever seeing a European. Also the few survivors from my community may well have moved away anyway. (The later European settlers used to find evidence of abandoned habitation which kind of fed the "this cleared land is gifted to us by God" bollocks, not getting that it had been gifted to them by disease)


But yes it famously goes Africa*->Europe/Asia->New world in terms of whose diseases kill who, best. Because human vs. disease in Africa is a grudge match where both sides have been interacting for a very long time! And as per Gwyain's important point a lot of domestic Zoonosis going on in Africa for a long time as well!



*generally speaking Sub-Saharan in this context as there was a lot of communication between N.Africa and Europe for a long continuous time, but this is all a generalisation and the specific matters, East Africa is different from West Africa etc, etc
 
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There also matter of Genetic Diversity. Native Americans had tiny founder populations, which cross Beringia through land or water to America. Eurasian populations had much larger founder, which cross Red Sea to Eurasia. with limited genetic diversity in its gene pool, Native American is more susceptible to disease.
 
Its factually wrong to say that Europeans were not affected by new world diseasesHave you not heard of Syphillis?
True, though the impact of syphilis was utterly insignificant compared to that of measles, smallpox, cholera , mumps, bubonic plague et cetera.


As has been said the reason is last of cities, the breeding grounds of disease, and the lack of domesticated animals, the source of most plagues. I'm surprised no-one has mentioned C. G. P. Grey yet.

There was an interesting alternate Earth for GURPS called Jenner-1 where
a proto-Cheyenne genius domesticated one of the last American horses about 8000 BC rather than spearing and eating it
and hence
...the Americans nevertheless produced an impressive urban civilization by 1492, one about equivalent to the early Roman era on the other side of the Atlantic. When Columbus and Pinzon opened up the New World, Europe gave the Americas smallpox, measles, and influenza as they did on Homeline. But the Americas returned cachexy, tetter rot, and the calenture to Europe.
 
True, though the impact of syphilis was utterly insignificant compared to that of measles, smallpox, cholera , mumps, bubonic plague et cetera.


As has been said the reason is last of cities, the breeding grounds of disease, and the lack of domesticated animals, the source of most plagues. I'm surprised no-one has mentioned C. G. P. Grey yet.

There was an interesting alternate Earth for GURPS called Jenner-1 where
and hence
Hmm I get it now.
 
Plausible hypotheses for one-sided disease effect:

- Like some have suggested, just not that many Native Americans with "low counters" closer to correct. I'm hopeful DNA analysis will eventually solve this question.
- Already mentioned low domestication levels limiting zoonosis a bit.

But would say there are some other plausible to me ideas:

- Idea of "Clean Siberian Filter"; in this model founding NA population didn't have many of the long standing pathogens epidemic in humans, so hard for more virulent forms to evolve once high population growth gave new niche.
- American animals more isolated from Old World primates for longer, so harder for zoonotic crossover to happen from non-domesticates (pathogens not as evolved for crossover to primates?).
- Low HLA diversity in Americas may have meant any NA pathogens which did evolve simply couldn't gain much traction in Eurasia with high HLA diversity. (Very speculative!)
- Different patterns of density; if American populations were much intensively clustered but not as extensively large, they would be hit harder by Eurasian diseases than converse (big low density pre-Columbian cities and little depth of population in hinterland might have been "perfect storm" of vulnerability).

So a mix of some other possible constraints on pathogens, and that there may have been some NA pathogens that we haven't identified, and they simply weren't that big a shock (because of general difference in social and immune system robusticity to disease) .
 
Occam's Razor. The Americas were a virgin disease pool as opposed to a consolidated Eurasian/African disease pool. Lacking a zoonotic pool of domesticate diseases, the Americas had no riposte to send to Eurasia/Africa. Syphyllis is debatable since it seems similar to yaws and Hansen's Disease, and in any event a single venerially communicable disease would not have the same impact as multiple easily communicable diseases.
 
The problem with the domesticated zoonosis hypothesis is that while some of the various virgin soil epidemics came from domesticates (e.g. cocoliztli is probably Paratyphi C, which probably originally comes from pigs, but is currently human-only), most did not, nor did most major (or present - coronavirus, Ebola, HIV, none are from domesticates) Old World disease outbreaks. Smallpox came from a terrestrial African rodent and was human-only. Y. pestis was from rats, for another prominent example.
 
Syphilis originated in the New World and was responsible for around five million deaths when it initially came to Europe. It remained a devastating disease until the invention of penicillin, with epidemics being frequent.
The origin of syphilis is disputed. The first identified outbreak occurred in Naples during the French siege of Naples in 1495. Spanish mercenaries fought on the Neapolitan side and some of them may have been to the New World. French soldiers definitely spread it when they went home.
There is skeletal evidence on both sides of the Atlantic that may indicate a presence in both Europe and the Americas before Columbus, but the evidence is not clear and subject to debate. It has even been suggested that the disease existed on both sides of the Atlantic before it was identified.
It might be satisfying to think that syphilis is the Natives' revenge on the whites; but it's just as likely that Spanish soldiers who served in Naples spread it as they later raped their way across the Americas.
 
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