Black Death Genes and Increasing Autoimmune Disorders

FOOD FOR THOUGHT:

 Genes that once protected our bodies during the Black Death, may now be increasing autoimmune disorders...

    An article from Harvard Medical School (HMS) details how genes that once protected our bodies during the Black Death in the 14th century, may now be increasing the prevalence of autoimmune diseases. Researchers have extracted the DNA of people who died during the time of the Black Death, and are using that to compare against the DNA of those who have lived through the COVID-19 pandemic (our time). From this data, they were able to deduce the fact that survivors of each pandemic carried genes that made them immune to the disease. This makes sense, considering the "survival of the fittest" philosophy introduced by Darwin, and due to evolutionary circumstances, it would make sense that those who survived one instance of a deadly disease could presumably survive another. The bacterium Yersinia pestis was known to cause the Black Death as it spread from animals to humans, and plays a role now, centuries later. The relevance comes into play with autoimmune disorders: those alive during our time with autoimmune diseases are more likely to carry those same infection-fighting genes that helped people survive the Black Death -- crazy right?

    This was a very fascinating article and it is interesting to see how the genes have been passed on evolutionarily through time. Not only that, but the human body has me awestruck. The things that it is capable of, such as passing on these genes that can prevent disease is so interesting to me. Furthermore, as someone with an autoimmune disease, I can't help but to wonder if I carry these same genes as well. I think it would be really fascinating to have my DNA extracted and compared to that of someone who survived the time of the Black Death, that way I could truly see if I am impacted by this phenomena. Selective pressures and immunity are quite interesting to me and I could see myself taking a deeper look into this topic in the future!

LINKS:

1. https://www.health.harvard.edu/blog/genes-protective-during-the-black-death-may-now-be-increasing-autoimmune-disorders-202212012859 

2. https://www.nature.com/articles/s41586-022-05349-x

Ancient Siberian DNA Reveals Plague

 

The picture above shows Lake Baikal where Siberians were infected with the plague bacterium, Yersinia pestis, about 4,400 years ago. A group of evolutionary geneticists extracted the DNA from 40 eastern Siberian human skeletons. From the 40 DNA samples, 2 of them contained the Yersinia pestis plague bacterium. The 2 skeletons dated back to 4,400 and 3,800 years ago. This data aligns with these two other studies very closely: Paleolithic to Bronze Age Siberians Reveal Connections with First Americans and across Eurasia  and Plagues plagued the Bronze Age. Researchers believe that ancient Siberians may haven been infected with version of Y. pestis that was not so harmful and virulent. Though this hypothesis has not been supported quite yet. In the end, this research has provided new insight on population shifts in that region. There has been research conducted in order to compare the ancient DNA from this region to present-day DNA from participants in Europe, Asia and North America. It was determined that ancient Siberias mixed several populations from within and outside of Siberia. It was concluded that this blending of populations occurred from the Late Stone Age to medieval times. Lastly, it was determined that the 2 ancient Siberians containing the Y. pestis in their DNA underwent large population changes during their lifetime. This genetic information is certainly fascinating and can be referenced when looking at ancient Siberian history. 

References 

Bower, B. (2019, August 08). Plagues plagued the Bronze Age. Retrieved from https://www.sciencenews.org/article/plagues-plagued-bronze-age

Bower, B. (2021, January 07). Plague may have caused die-offs of ancient Siberians. Retrieved from https://www.sciencenews.org/article/plague-bacteria-die-offs-ancient-siberians-genetics-dna

Yu, H., Spyrou, M. A., Karapetian, M., Shnaider, S., & Radzevičiūtė, R. (n.d.). Paleolithic to Bronze Age Siberians Reveal Connections with First Americans and across Eurasia. Retrieved from https://www.cell.com/cell/fulltext/S0092-8674(20)30502-X

Can teeth really show us evidence of plague?

Eske Willerslev and his colleagues, at the University of Copenhagen, in Denmark, began studying DNA from bacteria on teeth that caused plague during the Bronze Age and Iron Age. This time was marked between 4,800 and 3,000 years ago. Willerslev concluded the early plague germ, Yersinia pestis, was spread from person to person among the herders migrating across Europe and Asia during the Bronze Age. Coughing could have spread the plague, and if the germ caused a lung infection, the illness was considered pneumonic plague. If the blood of an individual became infected, it was considered septicemic plague.

            Willerslev and his team identified Y. pestis DNA on teeth from Bronze and Iron Age individuals. The DNA pieces showed up in seven of the 101 people. Two people with the strain were from Russia roughly 4,800 years ago. Another was from North Central Europe, 4,500 years ago. The third infected person examined was in West Asia from almost 4,200 years ago. Several more teeth collected were from Siberia and Poland and were 3,700 to 4,000 years old. The last sample was from an individual who lived in Armenia 3,000 years ago.

            From the evidence Willerslev and his team gathered, it is clear the germ spread over a wide area and for a large amount of time. Further investigation was concluded of the entire genome in the Bronze Age DNA. The analysis showed the earlier germ lacked the gene, which was present in the Iron Age individual. This gene allowed bacterium to survive in a flea’s gut. The plague germ would have been able to spread via flea bites at some point during 3,700 and 3,000 years ago.

            The biologists have compared plague DNA in one of the oldest Bronze Age individuals and the most recent Bronze Age individual and concluded both lacked a form of one plague gene that keeps an infected persons immune system from attacking the disease. This suggests that the earlier forms of the germ would have been vulnerable to attacks by the immune system. 

            One reason I found this article to be interesting was due to the time periods Willerslev and his team worked with. They collected and screened 89 billion pieces of DNA from teeth of individuals from the Bronze and Iron Age. That was almost 5,000 years ago! It is fascinating to know a scientist can pull ancient DNA from teeth of individuals that lived thousands of years ago. Another captivating point in the article mentioned this disease took over even when there really was no urbanization. But certainly this plague evolved and survived longer than expected. 

Plagues from another Origin

 The Justinian Plague and the Black Plague have been compared and contrasted for so long regardless of their 800 years distance from one another. The plagues affected millions of lives and resulted in ridiculously high death tolls. The questions remains whether or not the two plagues are related strains or if they are completely separate. A study done by Lancet Infectious Diseases showed incredible findings, however, through the extraction of DNA from two plague victims' teeth. They were able to reconstruct the genome and study the pathogens. The bacterial family Yersinia pestis is what both the Justinian Plague and the Black Plague hailed from, but the Black Plague is entirely different from the Justinian.

The two strains are both unlikely to be seen again, regardless of their origins. However, there is still no definite reason for the occurrence of the first or the resurgence of the second. There is evidence stating they both occurred after periods of much rainfall and resulted in climatic stability once the plagues were extinct. Perhaps it was the climate that created a perfect environment for such pathogens or the actual immunities of the people in these time periods could have been the reason. Either way, the authors who posted in the Lancet Infectious Diseases doubt another plague will ever arise.
http://www.latimes.com/science/sciencenow/la-sci-sn-plague-genetic-20140127-story.html