question: How come when Europeans came to America, diseases they brought wiped out huge portions of the Native populations, but diseases native to the Americas didn’t wipe out the European settlers?
comment: TLDR: Unlike their European counterparts, Native immune systems remained largely untested or exposed to disease in general. So, while some Europeans DID develop illness from American diseases, the inverse was just SO much worse. I actually know this. There are three reasons. 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. 3.Population densities were much greater in Eurasia, and there were more Eurasian cities than American cities. Cities were unhealthy placeswhere 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 Tenochtitlanapproached this.
passages: The spread of disease from European contact was not always accidental. Europeans arriving in the Americas had long been exposed to the diseases, attaining a measure of immunity, and thus were not as severely affected by them. Therefore, disease could be an effective biological weapon.
   The Native American population was devastated after contact with the Old World by introduction of many fatal diseases. In a well documented case of germ warfare involving British commander Jeffery Amherst and Swiss-British officer Colonel Henry Bouquet, their correspondence included a proposal and agreement to give smallpox-infected blankets to Indians in order to "Extirpate this Execrable Race". During the siege of Fort Pitt late in the French and Indian War, as recorded in his journal by sundries trader and militia Captain, William Trent, on June 24, 1763, dignitaries from the Delaware tribe met with Fort Pitt officials, warned them of "great numbers of Indians" coming to attack the fort, and pleaded with them to leave the fort while there was still time. The commander of the fort refused to abandon the fort. Instead, the British gave as gifts two blankets, one silk handkerchief and one linen from the smallpox hospital to two Delaware Indian dignitaries. A devastating smallpox epidemic plagued Native American tribes in the Ohio Valley and Great Lakes area through 1763 and 1764, but the effectiveness of individual instances of biological warfare remains unknown. After extensive review of surviving documentary evidence, historian Francis Jennings concluded the attempt at biological warfare was "unquestionably effective at Fort Pitt"; Smallpox after Pontiac's Rebellion killed 400,000–500,000 (possibly even up to 1.5 million) Native Americans.
   BULLET::::- Native American medical treatments such as sweat baths and cold water immersion (practiced in some areas) weakened some patients and probably increased mortality rates.
  
  BULLET::::- Europeans brought many diseases with them because they had many more domesticated animals than the Native Americans. Domestication usually means close and frequent contact between animals and people, which allows diseases of domestic animals to migrate into the human population when the necessary mutations occur.
   Thus both infectious diseases and populations tend to evolve towards an equilibrium in which the common diseases are non-symptomatic, mild or manageably chronic. When a population that has been relatively isolated is exposed to new diseases, it has no resistance to the new diseases (the population is "biologically naive"). These people die at a much higher rate, resulting in what is known as a "virgin soil" epidemic. Before the European arrival, the Americas had been isolated from the Eurasian-African landmass. The peoples of the Old World had had thousands of years for their populations to accommodate to their common diseases.
   In pre-columbian exchange times, a variety of diseases existed in the Americas. The limited populations and interactions between those populations (as compared to places like Europe), hampered the development of widespread, deadly diseases in the Americas. One notable disease of American origin is syphillis. The American era of limited disease would end with the arrival of Europeans in the Americas. European diseases and epidemics, while still present among Native American populations today, were especially influential in Native American life of the past. Diseases and epidemics can be chronicled from centuries ago when European settlers brought forth diseases that devastated entire tribes. Transitioning into more modern times, similar diseases still plague Native American populations. The current crises in diseases and epidemics are being addressed by many different groups, both governmental and independent, and are done through a multitude of programs.
   The European lifestyle included a long history of sharing close quarters with domesticated animals such as cows, pigs, sheep, goats, horses, dogs and various domesticated fowl, from which many diseases originally stemmed. Thus, in contrast to the indigenous people, Europeans had developed a richer endowment of antibodies. The large-scale contact with Europeans after 1492 introduced Eurasian germs to the indigenous people of the Americas.
   Disease killed the entire native (Guanches) population of the Canary Islands in the 16th century. Half the native population of Hispaniola in 1518 was killed by smallpox. Smallpox also ravaged Mexico in the 1520s, killing 150,000 in Tenochtitlan alone, including the emperor, and Peru in the 1530s, aiding the European conquerors. Measles killed a further two million Mexican natives in the 17th century. In 1618–1619, smallpox wiped out 90% of the Massachusetts Bay Native Americans. Smallpox epidemics in 1780–1782 and 1837–1838 brought devastation and drastic depopulation among the Plains Indians. Some believe that the death of up to 95% of the Native American population of the New World was caused by Old World diseases. Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no time to build such immunity.
   Because Native American populations were not previously exposed to most diseases introduced by European colonists, populations rarely had built up individual or population immunities to those diseases. In addition, Europe's position as a crossroads between many different peoples, many of whom were separated by hundreds, if not thousands, of miles (through things like constant war spreading localized afflictions throughout the continent, and the silk road bringing diseases from the East), resulted in Europeans being immune to a large variety of diseases. Therefore, the diseases, which were brought by the Europeans and had little effect on them, greatly affected, and often continue to affect, Native Americans. This phenomenon is known as the virgin soil effect.
   The trade of Native American captives, and the use of commercial trade routes continued the spread of disease. The diseases brought by Europeans are not easily tracked, since there were numerous outbreaks and all were not equally recorded. Suzanne Austin Alchon writes that “indirect evidence suggests that some serious illness may have arrived with the 1500 colonists who accompanied Columbus's second expedition in 1493. [...] And by the end of 1494, disease and famine had claimed two-thirds of the Spanish settlers.” The most destructive disease brought by Europeans was smallpox. The first well-documented smallpox epidemic happened in 1518. The Lakota Indians called the disease the running face sickness. Smallpox was lethal to many Native Americans, bringing sweeping epidemics and affecting the same tribes repeatedly.
   Over the 1st century and a half after Columbus's voyages, the native population of the Americas plummeted by an estimated 80% (from around 50 million in 1492 to eight million in 1650), mostly by outbreaks of Old World diseases.
   Before regular communication had been established between the two hemispheres, the varieties of domesticated animals and infectious diseases that jumped to humans, such as smallpox, were substantially more numerous in the Old World than in the New due to more extensive long-distance trade networks. Many had migrated west across Eurasia with animals or people, or were brought by traders from Asia, so diseases of two continents were suffered by all occupants. While Europeans and Asians were affected by the Eurasian diseases, their endemic status in those continents over centuries resulted in many people gaining acquired immunity.
   Encounters between European explorers and populations in the rest of the world often introduced local epidemics of extraordinary virulence. Disease killed part of the native population of the Canary Islands in the 16th century (Guanches). Half the native population of Hispaniola in 1518 was killed by smallpox. Smallpox also ravaged Mexico in the 1520s, killing 150,000 in Tenochtitlán alone, including the emperor, and Peru in the 1530s, aiding the European conquerors. Measles killed a further two million Mexican natives in the 17th century. In 1618–1619, smallpox wiped out 90% of the Massachusetts Bay Native Americans. During the 1770s, smallpox killed at least 30% of the Pacific Northwest Native Americans. Smallpox epidemics in 1780–1782 and 1837–1838 brought devastation and drastic depopulation among the Plains Indians. Some believe that the death of up to 95% of the Native American population of the New World was caused by Old World diseases such as smallpox, measles, and influenza. Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no such immunity.
   The natives of the Americas were faced with several new diseases at once creating a situation where some who successfully resisted one disease might die from another. Multiple simultaneous infections (e.g., smallpox and typhus at the same time) or in close succession (e.g., smallpox in an individual who was still weak from a recent bout of typhus) are more deadly than just the sum of the individual diseases. In this scenario, death rates can also be elevated by combinations of new and familiar diseases: smallpox in combination with American strains of yaws, for example.
  
  Other contributing factors:
   Viral and bacterial diseases that kill victims before the illnesses spread to others tend to flare up and then die out. A more resilient disease would establish an equilibrium; if its victims lived beyond infection, the disease would spread further. The evolutionary process selects against quick lethality, with the most immediately fatal diseases being the most short-lived. A similar evolutionary pressure acts upon victim populations, as those lacking genetic resistance to common diseases die and do not leave descendants, whereas those who are resistant procreate and pass resistant genes to their offspring. For example, in the first fifty years of the sixteenth century, an unusually strong strain of syphilis killed a high proportion of infected Europeans within a few months; over time, however, the disease has become much less virulent.
   By contrast, "Old World" diseases had a devastating effect when introduced to Native American populations via European carriers, as the people in the Americas had no natural immunity to the new diseases. Measles caused many deaths. The smallpox epidemics are believed to have caused the largest death tolls among Native Americans, surpassing any wars and far exceeding the comparative loss of life in Europe due to the Black Death. It is estimated that upwards of 80–95 percent of the Native American population died in these epidemics within the first 100–150 years following 1492. Many regions in the Americas lost 100%. The beginning of demographic collapse on the North American continent has typically been attributed to the spread of a well-documented smallpox epidemic from Hispaniola in December 1518. At that point in time, approximately only 10,000 indigenous people were still alive on Hispaniola.
   There was a fundamental difference in the human infectious diseases present in the indigenous peoples and that of sailors and explorers from Europe and Africa. Some viruses, like smallpox, have only human hosts and appeared to have never occurred on the North American continent before 1492. The indigenous people lacked genetic resistance to such new infections, and suffered overwhelming mortality when exposed to smallpox, measles, malaria, tuberculosis and other diseases. The depopulation occurred years before the European settlers arrived in the vicinity and resulted from contact with trappers.
  
  Section::::Colonial era.:Medical organization.
   Disease evolution and host pathogen interactions should be considered in Native American disease history. Disease evolution is the result of the interaction of the following parameters: hosts, parasites, and setting. Such an example of disease evolution is the direct biological effects of crowding that directly influences a host's susceptibility to disease. Research by Power et al. (1998) demonstrated that, at low doses of micro-bacterial pathogens, hosts were able to make an appropriate immune response and avoid tuberculosis; higher doses resulted in a less efficient form of a vaccination. The crowding that was a result of widespread relocation and concentration of native groups by the expanding America greatly impacted the susceptibility native people initially had to the foreign diseases.
   One of the most devastating diseases was smallpox, but other deadly diseases included typhus, measles, influenza, bubonic plague, cholera, malaria, tuberculosis, mumps, yellow fever and pertussis, which were chronic in Eurasia.
  
  This transfer of disease between the Old and New Worlds was later studied as part of what has been labeled the "Columbian Exchange".
   Before the Spanish discovered the New World (continental America), the deadly infections of smallpox, measles, and influenza were unheard of. The Native Americans did not have the immunities the Europeans developed through long contact with the diseases. Christopher Columbus ended the Americas' isolation in 1492 while sailing under the flag of Castile, Spain. Deadly epidemics swept across the Caribbean. Smallpox wiped out villages in a matter of months. The island of Hispaniola had a population of 250,000 Native Americans. 20 years later, the population had dramatically dropped to 6,000. 50 years later, it was estimated that approximately 500 Native Americans were left. Smallpox then spread to the area which is now Mexico where it then helped destroy the Aztec Empire. In the 1st century of Spanish rule in what is now Mexico, 1500–1600, Central and South Americans died by the millions. By 1650, the majority of New Spain (now Mexico) population had perished.
   During the 16th century, Spanish soldiers introduced smallpox by contact with natives of the Aztec capital Tenochtitlan. A devastating epidemic broke out among the indigenous people, killing thousands.
  
  In 1617, smallpox reached Massachusetts, probably brought by earlier explorers to Nova Scotia, Canada.” By 1638 the disease had broken out among people in Boston, Massachusetts. In 1721 people fled the city after an outbreak, but the residents spread the disease to others throughout the thirteen colonies. Smallpox broke out in six separate epidemics in the United States through 1968.
   Section::::European contact.
  
  The arrival of Europeans also brought on the Columbian Exchange. During this period European settlers brought many different technologies and lifestyles with them. Arguably, the most harmful effect of this exchange was the arrival and spread of disease or biological warfare; it was the genocide of entire civilizations.
   The Americas and Australia remained free of measles and smallpox until the arrival of European colonists between the 15th and 18th centuries. Along with measles and influenza, smallpox was taken to the Americas by the Spanish. Smallpox was endemic in Spain, having been introduced by the Moors from Africa. In 1519, an epidemic of smallpox broke out in the Aztec capital Tenochtitlan in Mexico. This was started by the army of Pánfilo de Narváez, who followed Hernán Cortés from Cuba and had an African slave suffering from smallpox aboard his ship. When the Spanish finally entered the capital in the summer of 1521, they saw it strewn with the bodies of smallpox victims. The epidemic, and those that followed during 1545–1548 and 1576–1581, eventually killed more than half of the native population. Most of the Spanish were immune; with his army of fewer than 900 men it would not have been possible for Cortés to defeat the Aztecs and conquer Mexico without the help of smallpox. Many Native American populations were devastated later by the inadvertent spread of diseases introduced by Europeans. In the 150 years that followed Columbus's arrival in 1492, the Native American population of North America was reduced by 80 per cent from diseases, including measles, smallpox and influenza. The damage done by these viruses significantly aided European attempts to displace and conquer the native population.
   Epidemics of smallpox (1518, 1521, 1525, 1558, 1589), typhus (1546), influenza (1558), diphtheria (1614) and measles (1618) swept the Americas subsequent to European contact, killing between 10 million and 100 million people, up to 95% of the indigenous population of the Americas. The cultural and political instability attending these losses appears to have been of substantial aid in the efforts of various colonists in New England and Massachusetts to acquire control over the great wealth in land and resources of which indigenous societies had customarily made use.
   After 1630, the initial areas of settlement had been largely cleared of Native Americans by major outbreaks of measles, smallpox, and bubonic plague beginning decades before the settlers began arriving in large numbers. The leading killer was smallpox, which arrived in the New World around 1510–1530.
  
  Section::::Colonial Era.:Characteristics.
   When Old World diseases were first carried to the Americas at the end of the fifteenth century, they spread throughout the southern and northern hemispheres, leaving the indigenous populations in near ruins. No evidence has been discovered that the earliest Spanish colonists and missionaries deliberately attempted to infect the American natives, and some effort was actually made to limit the devastating effects of disease before it killed off what remained of their forced slave labor under their encomienda system. The cattle introduced by the Spanish contaminated various water reserves which Native Americans dug in the fields to accumulate rain water. In response, the Franciscans and Dominicans created public fountains and aqueducts to guarantee access to drinking water. But when the Franciscans lost their privileges in 1572, many of these fountains were no longer guarded and so deliberate well poisoning may have happened. Although no proof of such poisoning has been found, some historians believe the decrease of the population correlates with the end of religious orders' control of the water.
  
raw_presuppositions: Diseases transferring from one population to another should transfer equally in both directions. Diseases transferring from one population to another should transfer equally in both directions.
raw_corrections: Europeans' immune systems had been tested and exposed to disease before but Native immune systems had not. Europeans' immune systems had been tested and exposed to disease before but Native immune systems had not.