[Petrochemicals (OP)]

When columbus landed in the Americas he and his peers brought with them the diseases of afro Eurasia with them. The native Americans where extremely vulnerable to these diseases, with population reductions of 99 percent within a few decades in probably the fastest and largest plague in history. Afro Eurasia faired far better, with only the contested claim of the great pox of Syphilis alleged to have come the other way. Why did the Afro eurasian not suffer cataclysmic annihilation from American diseases?

[alancalverd]

Relatively small gene pool, isolated for maybe 10,000 years, never acquired residual herd immunity (people often forget the word "residual" - you may have to kill 90% of the population to achieve it!), many deliberately infected in the later stages of colonisation, deprived of agricultural land and clean water, negligible provision of health services....you name it. 

[evan_au]

Measles has a nasty side-effect, even if you survive it: It resets your immune system.
So the adult population would have "forgot" all the immunities they developed as children against local diseases.

It is likely that many of the native American adults would have then succumbed to native American diseases.

[Petrochemicals (OP)]

Whilst the gene pool theory is plausible, i do not know whether it is credible. Gengis kahn is alleged to be the y chromosone of 1 in  200 men so if such practices occoured in the Americas over millennium, I suppose the gene pool could be problematic.

Neither of these answers state why a similar  effect did not occour though from native American diseases to the Afro eurasian world.

 

[SeanB]

I would say the ones that went back to Europe were finding a very wide range of hosts, all with large exposures to other diseases, so well prepared immune wise to a novel infection. Other way a long isolated population got a single exposure to a massive collection of diseases, all of them new to them, and with a population that was going to be more or less homogenous, so a vunerability would be present in many people to any disease.

Then add to this a deliberate spreading of disease by the settlers and governments later on, to get rid of what they regarded as a pest, and you can see why the native North American polulations were wiped out. Remember it is still less than a century ago that there was a payment for scalps on the statute books in a lot of places in the USA, and people claiming them as well.

[Petrochemicals (OP)]

I would say the ones that went back to Europe were finding a very wide range of hosts, all with large exposures to other diseases, so well prepared immune wise to a novel infection. Other way a long isolated population got a single exposure to a massive collection of diseases, all of them new to them, and with a population that was going to be more or less homogenous, so a vunerability would be present in many people to any disease.

Then add to this a deliberate spreading of disease by the settlers and governments later on, to get rid of what they regarded as a pest, and you can see why the native North American polulations were wiped out. Remember it is still less than a century ago that there was a payment for scalps on the statute books in a lot of places in the USA, and people claiming them as well.

Are you suggesting no diseases abounded in the Americas?

[SeanB]

Plenty of local infections, just the Europeans had so many new ones, and a population that constantly churned through new variants. The American continent, due to isolation for many centuries, and limited trade, had come to homeostasis with the native disease pool, but this new collection was going to be hard to counter, simply as they had no real selection previously for them.

[Petrochemicals (OP)]

Plenty of local infections, just the Europeans had so many new ones, and a population that constantly churned through new variants. The American continent, due to isolation for many centuries, and limited trade, had come to homeostasis with the native disease pool, but this new collection was going to be hard to counter, simply as they had no real selection previously for them.

Logic would dictate that what Eurasia experienced with disease in their isolation the Americas would likewise have done. Are you saying that the Americas where a disease mutation free area after their isolation?

[alancalverd]

Eurasia was genetically very diverse and had suffered innumerable plagues and pestilences by the time Columbus left these shores, so what was left of the population (after a very high rate of perinatal and infant deaths) was fairly resistant and understood some methods of quarantine and treatment for the diseases they exported. But they didn't export the treatment.

[Petrochemicals (OP)]

Eurasia was genetically very diverse and had suffered innumerable plagues and pestilences by the time Columbus left these shores, so what was left of the population (after a very high rate of perinatal and infant deaths) was fairly resistant and understood some methods of quarantine and treatment for the diseases they exported. But they didn't export the treatment.

There is no reason to doubt the genetic diversity of the americas, the fertility seemed reasonable. Plagues are also likely to limit diversity, only 10 percent of people are immune to HIV, probably related to each other in some way, a HIV pandemic would severely limit diversity. I would imagine diseases spreading in the Americas pre columbus too, similarly to Europe.

I say again why did the Americas not spread diseases to Europe, where they disease free? Is there a scientific basis to sacrificing people to the sun god atop a pyramid to protect your populace.

[evan_au]

I say again why did the Americas not spread diseases to Europe, were they disease free?

I think it is partly due to which group had the ocean-going ships.
- Europeans had the ships, and crossed the ocean from Europe to the Americas. They took various European endemic diseases with them (to which they were immune), and deposited them in a land which had no immunity.
- If Pre-Columbian Americans had crossed the Atlantic to Europe, carrying their endemic diseases, they may have managed to spread American diseases in Europe (if they weren't sunk by cannons first).

In fact, Columbus did take some Caribbean native back to Europe, but he would have taken the good-looking ones, not the sick and diseased.
- And they would have been quarantined and checked by doctors before they were paraded before the King of Spain.

[Petrochemicals (OP)]

I say again why did the Americas not spread diseases to Europe, were they disease free?

I think it is partly due to which group had the ocean-going ships.
- Europeans had the ships, and crossed the ocean from Europe to the Americas. They took various European endemic diseases with them (to which they were immune), and deposited them in a land which had no immunity.
- If Pre-Columbian Americans had crossed the Atlantic to Europe, carrying their endemic diseases, they may have managed to spread American diseases in Europe (if they weren't sunk by cannons first).

In fact, Columbus did take some Caribbean native back to Europe, but he would have taken the good-looking ones, not the sick and diseased.
- And they would have been quarantined and checked by doctors before they were paraded before the King of Spain.

The European plagues should have occoured larger on, but they did not and cortez should not have has such an easy time of it.

Ships where known to be disease carriers, many lower class sailors died on voyages from disease which is primarily why most people where so unwilling to become sailors. The quarantine of ships though should not have prevented a later spread through carriers who where immune.

[evan_au]

(disease) spread through carriers who where immune

I think there are 2 different ideas mixed up there:
- People who are immune have overcome the disease, and will not spread the disease
- Carriers are people who have not overcome the disease, but in lingers on in a chronic condition. They can certainly spread the disease.

For example,  the adult sailors who initially explored a new land did not carry smallpox, because it was endemic in Europe, and they were all immune.
- However, later settlers took babies (who were not immune), and smallpox could circulate on a ship among the non-immune children, carrying smallpox to new countries.
- This caused a problem when doctors wanted to carry a milder version of smallpox to the Americas, for use in "variolation" (a precursor to vaccination). So they drafted young orphans who had never suffered smallpox, and transferred smallpox from one to the next, in a chain stretching across the Atlantic.
- Later, bottles of dried smallpox blister were carried to North America, and used to infect blankets, which were given to the native Americans. One soldier who had seen this done in North America later came to the new colony in Australia - followed by an outbreak of smallpox among Australian aborigines.

[Petrochemicals (OP)]

(disease) spread through carriers who where immune

I think there are 2 different ideas mixed up there:
- People who are immune have overcome the disease, and will not spread the disease
- Carriers are people who have not overcome the disease, but in lingers on in a chronic condition. They can certainly spread the disease.

For example,  the adult sailors who initially explored a new land did not carry smallpox, because it was endemic in Europe, and they were all immune.
- However, later settlers took babies (who were not immune), and smallpox could circulate on a ship among the non-immune children, carrying smallpox to new countries.
- This caused a problem when doctors wanted to carry a milder version of smallpox to the Americas, for use in "variolation" (a precursor to vaccination). So they drafted young orphans who had never suffered smallpox, and transferred smallpox from one to the next, in a chain stretching across the Atlantic.
- Later, bottles of dried smallpox blister were carried to North America, and used to infect blankets, which were given to the native Americans. One soldier who had seen this done in North America later came to the new colony in Australia - followed by an outbreak of smallpox among Australian aborigines.

So are ebola survivors not immune? Survivors as you put it have been known to pass on disease months or years later.

[alancalverd]

Indeed, it may all come down to quarantine. European invaders just wanted to get on the land, with all their agues and poxes, but the port authorities insisted than anyone travelling east across the Atlantic should have a clean bill of health before disembarking.

[evan_au]

are ebola survivors not immune?

Ebola is quite a vicious virus, killing about half of those infected.
- If you don't overcome the virus, it kills quite rapidly
- So it becomes a race between your immune system generating effective antibodies - or the virus killing you first
- Like COVID, Ebola has genes that inhibit the body's innate immune system, allowing it to take over more quickly
- Ebola directly attacks macrophages (white blood cells), which form part of the immune system
- Before a vaccine was available, they used recovered patients to nurse the sick - they didn't need such fancy protective equipment
- They also tried antibody transfusions from recovered patients, to keep the virus under control until the patient could generate their own antibodies.

These days, ring vaccination is used on anyone who may have come into contact with an ebola patient.
- This is difficult to administer, since there is an ongoing uncivil war in the area...
See:  https://en.wikipedia.org/wiki/Ebola

[Petrochemicals (OP)]

Indeed, it may all come down to quarantine. European invaders just wanted to get on the land, with all their agues and poxes, but the port authorities insisted than anyone travelling east across the Atlantic should have a clean bill of health before disembarking.

At very least then the invader and colonists should have been blighted in a similar fashion to the native populations, but as mentioned previously, cortez did not suffer in a similar fashion to montezuma.

The gene pool  theory looks most likely alan, as in the case of gengis Kahn, but over millenniums. If the king and his issue take 1000 wives each for many thousand years that would create a very narrow genetic group.

[Bored chemist]

What was the population density like in Pre-Columbian America?

[alancalverd]

On the low side of negligible.

[Bored chemist]

A lot of the diseases mentioned are typically found in areas with high population densities.