Why did Native Americans die of European diseases while Europeans didn't have serious diseases from the New World?

I read that most Native American victims of colonization in the new world died of European diseases and not by battles. But why didn't European people catch some deadly disease from Native Americans?
Was it because of better European immunity?
Was it because Europe had better experience handling diseases?
Or what factors played major roles in this historical exchange of bacterias and viruses?

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    Related: biology.stackexchange.com/q/20731/975. – TRiG Feb 25 '15 at 18:41
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    Europeans did catch very serious deceases in the New World. In particular in West India. Yellow fever is one such decease. – Alex Feb 25 '15 at 20:38
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    It is still disputed whether syphilis was brought to Europe from America or the other way around. But a terrible epidemic of syphilis stroke Europe in XVI century, immediately after the discover of America. – Alex Feb 25 '15 at 20:42
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    Nevertheless yellow fever was a major killer of Europeans in the West India, as historical records show. – Alex Feb 25 '15 at 20:47
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    @Alex: Right, but they didn't catch yellow fever from the Native Americans (like OP asked). They caught yellow fever from the African slaves they brought to the New World. – two sheds Feb 25 '15 at 20:55

Europeans were introduced to at least one important disease from the Americas (syphilis), but far more Old World pathogens were introduced to the Americas than vice versa. There are several reasons for this imbalance.

  1. European agriculturalists lived in closer proximity to disease vectors than did most Native Americans. A number of important diseases started with pigs, fowl, and so on before making the leap to humans. The Americas had fewer large mammals than did Eurasia, and so there were fewer candidates for domestication. Accordingly, American agricultural communities picked up fewer diseases than did Eurasian agricultural communities.

  2. Europeans were part of a much larger human community than the Native Americans. Europeans had already been exposed to Chinese pathogens from at least the 6th century AD. The high volume of trade in the Mediterranean and the Indian Ocean over the next millennium meant that Eurasia was, from the perspective of many pathogens, a single community. Diseases like the plague could travel from Asia to Europe more easily than a pathogen could travel up and down the Americas. This is in part because the East-West axis had more similar climatic conditions than the North-South axis. Eurasian trade also involved sailing vessels, which carried rodents. Rodents were some of the nastiest disease vectors, and plagues often originated in port towns because of these stowaways. For all of these reasons, 15th-century Europeans (and their ancestors) had experienced a wider variety of germs than had their American counterparts.

  3. Population densities were much greater in Eurasia, and there were more Eurasian cities than American cities. Cities were unhealthy places where diseases could remain "endemic" in the human or rodent population. By some estimates, a disease like measles can only be sustained in cities with a population over 500,000. In the Americas, only Tenochtitlan approached this. American pathogens might die out due to lack of "reservoirs." For example, there was at least one plague of American origins that killed from 7-17 million Mexicans in the 16th century. After killing 80% of the native population, the disease simply disappeared. We actually have very little idea what this disease was, or if it could appear again.

  4. The long history of epidemics, plus the presence of disease reservoirs in European urban communities, did mean that natural selection on disease resistance was a larger factor in Europe than in the Americas. Europeans had better immunity to most communicable pathogens than Americans (see @MasonWheeler's excellent answer), which also made them "better" disease vectors.

Of course, Eurasia was not the only Old World disease reservoir: African pathogens like that responsible for yellow fever were able to establish themselves in the American tropics. In these cases, it was the African slaves who had acquired resistance to the disease. While Europeans may have suffered from African pathogens along with the native Americans, these still go into the ledgers as Old World diseases, and they just make the imbalance of the Columbian Exchange all the worse.

All of this can be read about in more detail in Jared Diamond's Guns, Germs, and Steel. Also, read the comment thread here, where @Himarm and @Odysseus in particular make some good points pushing back against my answer.

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    Which logic applied in the same way only negatively when the Europeans came to the Indian sub-continent. Most of them were so sick much of the time. – Rajib Feb 25 '15 at 14:09
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    The biggest thing, is the relation to animals over every other factor, The native americans had Lamas, thats about it, and they lived far outside of urban areas, they had no cows, pigs, horses, sheep, goats, some fowl. europe, china, the middle east all had very close contact with some or all of these animals for thousands of years, this is the single factor that increased disease resistance for europeans over the native americans, The native Americans also lived in very large metropolitan areas, with fairly dense populations, throughout all of central-south america. from fully populated – Himarm Feb 25 '15 at 15:06
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    +1 for mentioning Guns, Germs, and Steel; this very question was a significant part of the opening chapters – jhocking Feb 25 '15 at 19:23
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    @Himarm You are not considering the climate variations that came into play just before the Europeans came, these lead to reduced food production in the Americas, mostly through drought. Famine caused by these droughts would decrease disease immunity and lead to death in the population. While the European diseases are often taunted as being mass killers, which they were, there are other factors that produced the massive deaths in the native american population, such as climate variations and land infertility. Source: 1491 : New Revelations of the Americas Before Columbus, by Charles C. Mann – BOB Feb 26 '15 at 15:37
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    @Odysseus: I've read plenty of work that supports the higher estimates for the population of Americas and what's more, I believe them. But even with the higher estimates, American population densities just don't compare to Europe, India, or Asia. I know there was long-distance trade in the Americas, but again, it was not as intense as in Eurasia. My answer really doesn't imply any denigration of the American civilizations. – two sheds Feb 26 '15 at 22:34

Several good answers have already been suggested, but there are a few very important points that are worth mentioning: Native Americans were badly unprepared for the emergence of epidemic disease among their populations, both genetically and culturally.

According to this article from 2002, there was a major genetic component to it: far less immune system biodiversity among Native Americans than Old Worlders.

Indigenous biochemistry may also have played a role. The immune system constantly scans the body for molecules that it can recognize as foreign—molecules belonging to an invading virus, for instance. No one's immune system can identify all foreign presences. Roughly speaking, an individual's set of defensive tools is known as his MHC type. Because many bacteria and viruses mutate easily, they usually attack in the form of several slightly different strains. Pathogens win when MHC types miss some of the strains and the immune system is not stimulated to act. Most human groups contain many MHC types; a strain that slips by one person's defenses will be nailed by the defenses of the next. But, according to Francis L. Black, an epidemiologist at Yale University, Indians are characterized by unusually homogenous MHC types. One out of three South American Indians have similar MHC types; among Africans the corresponding figure is one in 200. The cause is a matter for Darwinian speculation, the effects less so.

It also points out that, when serious disease struck, Europeans knew how to handle it and Native Americans did not, which just made it worse for them:

Having little experience with epidemic diseases, Indians had no knowledge of how to combat them. In contrast, Europeans were well versed in the brutal logic of quarantine. They boarded up houses in which plague appeared and fled to the countryside. In Indian New England, Neal Salisbury, a historian at Smith College, wrote in Manitou and Providence (1982), family and friends gathered with the shaman at the sufferer's bedside to wait out the illness—a practice that "could only have served to spread the disease more rapidly."

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    Nice article. I'm surprised that they say that the cause is a matter for speculation. I thought American Indians just had lower genetic diversity in general, due to the population bottleneck at the time of migration to the Americas. But I know next to nothing about genetics, so that could be an oversimplification. – two sheds Feb 25 '15 at 17:52
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    +1 it answers one of my subquestions "Was it because Europe had better experience handling diseases?" – CsBalazsHungary Feb 26 '15 at 9:14
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    They were not any better at handling disease anymore than the native Americans... they were better at preventitive measures. True serums and vaccines did not exist until about the beginning of the 1900's, when medical knowledge and tech exploded expotentially. – Epiphany Feb 26 '15 at 17:19
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    @Epiphany: And those "preventative measures" are a form of handling disease, on a societal scale if not a personal one. – Mason Wheeler Feb 26 '15 at 17:59
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    @dsollen European cultural understanding of the idea of quarantine actually dates back thousands of years; you can find the basic principles laid out in the Law of Moses. And they didn't need to understand all the "important details" or have a scientifically accurate Germ Theory to understand that contagion--the spread of disease from an infected person to a healthy person--exists, and that preventing contact with an infected person is thus a good way to prevent healthy people from contracting the disease. – Mason Wheeler Feb 2 '16 at 20:02

Certainly some diseases are of New World origin.

The Old World had more diseases and more deadly diseases simply because the population was much greater and in certain place more concentrated.

It is likely that more New World natives were killed by disease than by violence. However, this is just as true in the Old World: many more have died of disease than by war.

It is reasonable to assume Old World inhabitants have more developed immune systems, being in a more disease-intensive place, however as far as I know this is unproven. It is difficult to measure the "quality" of an immune system. Certainly, some people are more resistant to illness and others tend to be sickly, but the reasons for this are unclear.

There is a significant environmental aspect to illness. Tropical regions, for example, harbor many more diseases than temperate regions. Serious contagious illnesses are usually transported by a vector of some kind, so interaction with the vector may be more important than immune response.

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    there is almost universal acceptance that the Europeans increased immunity came from living with domesticated animals, as there were no domesticated animals in the entirety of north/south american, but the lamas that the inca's had, and they were kept far from urban areas, not milked, and lived in small groups. NA/SA also had no pigs, cows, horses, as all of these animals were from the old world, so the native Americans didn't have any animals to domesticate. – Himarm Feb 25 '15 at 16:40
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    @TylerDurden en.wikipedia.org/wiki/Cowpox, for example. – Digital Trauma Feb 25 '15 at 17:12
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    @TylerDurden "His patients who had contracted and recovered from the similar but milder cowpox (mainly milkmaids), seemed to be immune not only to further cases of cowpox, but also to smallpox". Perhaps not a bulletproof, scientific proof, but the implication is that the milkmaids (who presumably have more contact with animals than the general population) are in fact not only immune to cowpox, but also to the much more dangerous smallpox. – Digital Trauma Feb 25 '15 at 18:16
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    @TylerDurden it's a bit the other way around - living with animals means that you get more diseases, as many of the historical and current epidemic diseases are of an animal origin. This means that if community A lives with animals and community B doesn't; then community A will have a bunch of diseases that they have adapted to but that are deadly to B, but community B won't have produced as much of those "biological weapons" – Peteris Feb 25 '15 at 19:51
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    @TylerDurden even the old Guns, Germs and Steel discusses it in detail; but many diseases that are species-specific now have originated in animals. Off the top of my head, plague, HIV, smallpox, flu and ebola have all mutated from animal diseases. Perhaps to be more clear - I'm not neccessarily saying that a family living with animals will get more disease infections in short term; I meant that a civilization that lives with animals will in long term see more new types of diseases originating from those animals. Swine flu can originate only if you have many pigs in contact with people. – Peteris Feb 25 '15 at 20:06

I'd say the syphilis was was quite a deadly illness contacted from the Native Americans. They were immune to it (wonder if they still are…).

Although it is not 100 % historically proved that the syphilis originated from the New World, it started spreading like crazy after its discovery.


If you get sick and bring your disease to the place you are going (for instance, because you were on a long and exhausting journey), you are going to be ill at your destination. You may have carried the germ for a long time, since you are used to it, and it will only strike if/when you are weakened.

If you get sick at your destination, it is not likely that you are allowed on board for the voyage back.

The only way a disease is going to make it back to your origin, is if it incubates longer than the time it takes you to board the ship and sail home, or if it incubates long enough to cause an infection spreading in the ship, but not wipe out the ships population.

Looking at the duration of the Atlantic voyage, this may pose serious constraints on the last scenario. More people are likely to get sick in the destination country. If only one party is traveling, this skews chances. Native Americans did not travel to Europe as far as I know.

Of course, travel over land is not isolated in the way a ship is and will have far fewer constraints.

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    The problem with this is lack of knowledge back in those times, and also I would note that many diseases are not very visible in the first days, so it is easy to imagine that a sick person travels on a boat and his situation gets way worse during the travel and passes the disease to the fellow sailors on route. – CsBalazsHungary Feb 26 '15 at 12:02
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    This does not take into account carriers, that do not get sick themselves, yet are highly contagious without showing symptoms. They would fly right under the radar. – Epiphany Feb 26 '15 at 17:07
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    Interesting set of opinions, but I think we need some sources to evaluate this hypothesis. – Mark C. Wallace Feb 27 '15 at 15:22
  • they did actually, consider Pocahontas for one, who is buried in the UK – bigbadmouse Oct 4 '19 at 7:37

One of the biggest considerations, although hypothetical and not talked about, is simply the water. A great number of diseases and plauges during this era were due to waterborne pathogens. Europeans rarely drank plain water during the period, and you were more likely to find them drinking beer, wine, and mead just for this reason. It was commonly diluted into their water supplies as well, because the alcohol killed of the majority of the pathogens.

This is quite contrary to the newly explored western worlds natives at the time, who relied on the purity of their water. In short, it could be quite possible that Europeans introduced pathogens into their water supply that they had not had time to develop immunities to. This seems quite more plausable than other scenarios speculated about this subject. Early biological warfare.

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    "because the alcohol killed of the majority of the pathogens". No- mixing alcohol in water will not protect you from water-borne pathogens. – Rajib Feb 26 '15 at 11:54
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    No- I'm not coming at you at all. It's just that scientifically that's not correct. But if you can cite the links to the historians who observed alcohol protects from pathogens, do add the links. BTW, drinking beer as a substitute is not the same thing as adding alcohol to water. – Rajib Feb 26 '15 at 15:43
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    Please take a look around History Stack Exchange. We comment to elicit better answers. There are no personal friends/foes. I mentioned because you said "more likely to find them drinking beer". Links to sites and resources are also the norm here. Please note that when you provide the links I will upvote your answer. I don't judge your intelligence at all, and I'm not being nasty. Cheers. – Rajib Feb 26 '15 at 16:05
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    @Rajib. I just gave you a full page on this topic right here on HSE. Is that not enough of a verification on cited information? And I was relaying what historians have agreed upon when I said 'likely to find them drinking beer', as I was not the one that did the historical research that produced that determination. Personally, I think they drank merely because they liked to get drunk, if you want to know what I personally think. – Epiphany Feb 26 '15 at 16:12
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    Let us continue this discussion in chat. – Rajib Feb 26 '15 at 16:13

I've read that Africa contains populations of bacteria that have been co-evolving with our ancestors for tens of millions of years and are able to survive all of Homo Sapiens' immune systems' defenses as well as those of other primates. Most of these are harmless, but they form a reservoir of human-adapted germs from which new desease strains can come. Other regions including the Americas don't have any comparable source of new diseases that can infect humans.

Sorry, I don't have the source for this. If true, it would explain why few or no major human diseases have their origins in the Americas, which I believe was the original question.

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    This would certainly benefit from some supporting documentation references as it seems to be a flimsy theory without. – KillingTime Sep 28 '18 at 6:00

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