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Thanksgiving and Immunity

This Thanksgiving, let’s take a moment to look at the colonization through the lens of public health by examining the impact that intercontinental travel and first time contact with outside populations had on European settlers and the established Native American tribes in the Americas throughout the 15th to the 19th centuries.

Before contact with the Europeans, Native Americans suffered relatively few diseases (in comparison) and were generally very healthy. This is largely due to their culture and lifestyle. Native Americans did not often live in as close quarters as their European counterparts, giving infectious diseases fewer avenues to thrive and spread from person to person. Additionally, their culture supported the sharing of food and resources. This meant that very seldom did someone in a tribe go hungry or become malnourished because it was a source of pride and culturally normal to display wealth by sharing crops and resources with less fortunate tribe members. It is also important to understand that Native Americans did not domesticate animals in the same way that Europeans did. This reduced the opportunity for zoonotic infections to jump from animal hosts to human hosts. As a result, the prevalence and types on infections that permeated the communities in the Americas were inherently different than the landscape of European diseases. In the article “Health Conditions Before Columbus: Paleopathology of Native North Americans” indicates that while the Native American populations already experienced infectious diseases and chronic conditions, there are numerous diseases that caused epidemics upon the “discovery” of the New World by European explorers. Examples of “diseases that were not present in the Americas until contact include bubonic plague, measles, smallpox, mumps, chickenpox, influenza, cholera, diphtheria, typhus, malaria, leprosy, and yellow fever.” (Side note: You can read about the eradication of smallpox on the blog here!)

Many of the infections brought to North America by European settlers were completely foreign to the natives. As a result, these populations lacked immunity or sufficient resources to fight infection. Many of the most devastating infections from across the Atlantic were diseases that stemmed from the cramped living quarters in cities and contact with domesticated animals. The diseases spread among trade routes and other avenues, affecting many native populations long before they ever came into contact with the European explorers. The article “The Cultural Implications of European Disease on New World Populations with Primary Focus on the Abenaki, Powhatan, and Taino Groups” indicates that “the population of the American continents may have fallen by 90 percent between the beginning and end of the 16th century.”

The implication of these disease exposures was one of the largest unintended upheavals of human population in recent history. And while infectious diseases are known to be large factors in shaping the course of human history and evolution, this historical event was largely unprecedented in that is virtually pitted one evolutionary line against another in an “Old World versus New World” sort of fashion. In fact, an article in Science Magazine indicates that due to exposure to new illnesses, specifically during the occurrence of a smallpox outbreak approximately 175 years ago, there was a genetic shift in the genome of the Native American population. What is significant about this shift is that the change occurs in the portion of the genome responsible for the composition and function of our immune system. It appears that there was some sort of genetic selection occurring that had a huge impact on our genome as a population. Due to the increasing globalization since that time, the article states that there are some relatively new (in the history of living species) genes that appear with almost 100% in the human genome that were not as prevalent almost 200 years ago.

While there is infinitely more we could do to delve into this topic, a brief reminder of the unique history of the Americas, particularly as it pertains to our health. Today, have a happy thanksgiving and be thankful for your amazing immune system!

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