As we discussed in class, the appearance of plagues occurred as a result of the transition between hunter-gatherer and sedentary lifestyles. With help from the text and articles provided in Canvas, I separated the changes made by this transition into three distinct factors: closer proximity to other humans, closer proximity to animals, and more opportunities for interaction with disease carrying pests. Historical and contemporary examples of each of these factors provides insight into how plagues appeared in history, as well as how modern human impact continues to shape the development of infectious diseases.
When hunter-gatherers became sedentary, they formed communities that created close interpersonal interaction. People spent more time in close quarters with others daily, and it became easier for diseases to be passed from one infected individual to an entire group in a short period of time. One example of this was the 1918 “Spanish Flu” influenza outbreak, where newly prosperous cities like Philadelphia were hit hardest by the disease due to the densely packed areas of people. The influenza film we watched in class emphasized that large gatherings like rallies and drives for the war effort brought people in close quarters, allowing for much more physical contact and facilitated spread just as clan gatherings or rituals would in ancient societies. Furthermore, settlements formed by the new sedentary lifestyle were not efficient with waste disposal. Even in modern times, as mentioned in the article “American Epidemic” (by Melinda Moyer, published in Scientific American in 2018) large cities like Hong Kong can have trouble maintaining public sanitation and hygiene. A small U-shaped bend in the bathroom ventilation pipes of the building harbored the SARS virus and facilitated its spread, leading to a SARS outbreak based in the city in 2003.
The second factor introduced by a transition from hunter-gatherer to sedentary life was increased interaction with animals. Domesticated animals became reservoirs for human disease. One example from the PowerPoints in class is cows, who served as a reservoir for smallpox in the from of the cattle disease rinderpest. Even house pets like domesticated dogs can carry and transmit rabies to humans, fortunately a lot less common in modern times due to vaccines developed during the 20th century, as described in the CDC article “Control of Infected Diseases- Achievements in Public Health 1900-1999” provided in class. Another example of animal-human interaction causing disease is the spread of Nipah from bats to humans, as described in the film “Spillover”. Collection methods for date palm juice by humans allowed for bats to drink or even urinate in the collected juice, leading to human infection which spread by saliva to the rest of the community and causing a 2004 epidemic in India.
The final factor in causing human disease with a sedentary lifestyle is increased interaction with pests. Some pests are carried by domesticated animals (like fleas on cats or dogs), while others simply established a home for themselves amongst the newly established sedentary cities. One historical example is schistosomiasis or “pharaoh’s plague”, as it is described in the text (The Power of Plagues by Irwin Sherman, published 2017) as originally affecting ancient Egyptian settlements due to their construction of irrigation ditches. The parasite reservoir was a small snail living in the ditches, and people were infected by skin contact of the parasite entering the body, breeding inside, and ejecting their progeny back into the water source via human feces. Modern human impact includes the increased geographic range of such diseases, both by rising global temperatures (expanding the area in which the schistosomiasis worm can survive) and increased global travel by humans (allowing for infected individuals to transmit a disease to people farther away from patent zero). Another example of this increased geographic range is described in the article “Catching Fever” (by Lois Parshley, published in Scientific American in 2018). Rift Valley fever is transmitted by mosquitos and was originally identified in 1931 as being restricted to southern and eastern Africa. In 1977, however, the disease was found to have migrated north to Egypt, and then on to Saudi Arabia and Yemen, where it continues to be a potential threat today.
Modern concerns about facilitated disease spread due to increased globalization and global warming bear striking similarities to historical examples of facilitated disease spread due to hunter-gatherer’s transition to a sedentary lifestyle. The potential for a global epidemic, as was narrowly avoided in Lagos with Ebola in the film “Spillover”, means that human technology will need to adapt to protect its citizens in the future, just as it did to develop modern sanitary and medical practices to combat the plagues of the past.
HR: References as listed in the text, class discussion, spelling/grammar check by Microsoft Word