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The Role of Infectious Diseases within History

Microscopic in size but enormous in impact

Viruses and bacteria have accompanied human´s history from its very beginning. Since the shift to agrarian life 10,000 years ago infectious diseases increased dramatically and pandemics happened: More and more people lived close to each other and to animals, often under poor sanitation and nutrition, which are the perfect circumstances for viruses and bacteria to grow and spread. Among these early viruses and bacteria were illnesses such as malaria, tuberculosis, leprosy, influenza, smallpox, measles and polio.

How human assistant the spread of infectious illnesses

Mankind mainly supported the spread of infectious illnesses with urbanization, agriculture and globalization.

  1. urbanization

People moved closer together and interacted with other towns and cities through trade but also war. Furthermore, the increase in population pressured the environment.

  1. agriculture

In the Neolithic Age, with the domestication of animals and the development of agriculture animal and plant viruses, especially in monocultures, started to effect human´s lives: Animal viruses so-called “epizootics” particularly on livestocks harmed humans as they killed the domesticated animals, which were the basis for the people´s lives and could so cause famine. But even worse viruses could cross from animals to humans in form of zoonotic infections. Examples for zoonotic infections are the influenza virus that crossed from ducks and waterfowls to pigs and finally to humans. In the 20th century HIV came from chimpanzees and in the 21st century the Ebola virus probably from bats and Marburg from monkeys.
Plant viruses mostly occurred due to ecological changes caused by humans: E.g. when crops were cultivated in country where they were not found before. Historic examples are the potato leafroll virus and a tulip virus: The potato leafroll virus caused the Irish Great Famine in the 1840s destroyed a considerable amount of the potatoes in Ireland. As a result, around one million of Ireland´s inhabitants died and another million emigrated, especially to the US. After the famine the population had dropped between 20-25%.
The tulip virus, on the other hand, caused an enormous economic crisis: During the tulip mania in the 1930s one bulb could cost as much as a house and tulips with strips were highly popular. But these strips were caused by a virus which humans accidentally transferred from jasmine to tulips.  So a virus “killed” the stock market in the Netherlands.
That is why nowadays, many countries have strict importation rules and controls to prevent the spread of plant viruses and insects from the plants.

  1. globalization

Cities started to trade with one another, people travelled to other places, war and the aim of expanding the power of cities, regions and countries let to an increased interactivity and enabled the spread of diseases.
Infected turned home and spread the disease there too or brought diseases to other territories: European colonists brought diseases, like measles, smallpox and influenza, to the Americas and Australia between the 15th and 18th centuries. That had tragic effects on the local population as they had no natural resistance: Smallpox weakened the Aztec capital Tenochtitlan to such an extent that the Spanish Conqueror Hernán Cortés could take the capital with fewer than 900 soldiers and conquered Mexico. All that would have been impossible without the microscopic “supporter”: smallpox. In the following years more than half of the native population died due to the imported diseases. So it were viruses and bacteria that helped European colonists in their conquering.

Records on infectious diseases

It needs to be said that not all viruses are a threat: E. g. Humans got used to Herpes viruses. Reports on such milder viruses are seldom as the focus in history records was set on epidemics and pandemics.

One of the earliest records of viral infection is on an Egyptian stele from the 18th Dynasty (1580–1350 BC) and shows a foot that was deformed by the poliovirus.

A poliovirus victim from 18th Dynasty (1580–1350 BC)
https://commons.wikimedia.org/wiki/File:Polio_Egyptian_Stele.jpg

Records of pre-modern times need to be read with caution because till medicine became a science, the description of diseases was rather vague.

Diseases as “god-sent”

Many ancient societies believed that diseases were sent by spirts and gods as punishment: In Greek mythology Pandora´s box was a punishment that Zeus sent after Prometheus stole fire. Zeus instructed Pandora to give the box to mankind but to warn them not to open it as it was filled with sickness, death and other evils. As Pandora opened the box all those evils entered and changed the world. Luckily, “hope” stayed inside the box. So there is still hope for mankind.
In the Bible god sent 10 plagues to free his people from slavery in Egypt: The 5th plague was on livestock and killed horses, donkeys, camels, cattle, sheep and goats. The 6th let to boils on men and animals and the 10th killed all firstborns.

Medieval Times

The most famous disease of the Middle Ages was the “Black Death”, a bacterial infection with “Yersinia pestis”, that took the half of Europe´s population. But also smallpox, measles and rinderpest let to many deaths.

In the Middle Ages any disease was very risky for the patient as the physicians had limited medical knowledge, believed in superstition and used bizarre medicine.

Changes within viruses and the human

Over time viruses adopted: There very many influenza pandemics as the virus often undergoes genetic shifts but none of its outbreaks was that harmful than the “Spanish flue” in 1918, when around 50 million people died around the world and India was its epicenter with 20 million deaths.

Beside the “classic” infectious diseases new ones emerged in the 20th and 21st century, such as SARS and HIV. These new viruses have the advantage that they can spread easier to due the high level of urbanization and globalization.

But also the human body adopted to viruses and bacteria and got immune against some.

… still vulnerable

Humans developed various coping strategies against infectious diseases: From vaccines and antiviral drugs against some viruses to antibiotics against bacteria. Furthermore, the understanding of such diseases improved enormously, which helps to keep the death rate low.

Historical tactics such as social distancing and isolation of the infected in quarantine, restriction on trade and travel still work today and are used to limit the impact of infectious diseases.

But as COVID-19 shows humans and their environment are vulnerable: Especially the economy as such diseases mainly mean one thing, which is uncertainty. These uncertainty of when and how it will end lets to panic by some. The long-term effect of the coronavirus can not be seen now but a more digitalized world seems to come.

In such crisis conspiracy theories and fake news, blaming (and punishing) certain groups in society and stigmatization happen.

COVID-19 proofs that even in modern medicine humans can not control a virus from becoming a pandemic. Till a cure or vaccine is found the magic words are: distance and hygiene, two concept that go back to the pioneers in medical science in the 19th century.

For modern medicine and society stay many challenges concerning future infectious diseases:

  • With the help of globalization and digitalization modern medicine and science need to find new vaccinations against viruses and antibiotics, as many bacterial infections and humans became resistant to many antibiotics.
  • Research and politics need to make sure that viruses and bacteria are not used as bioweapons.
  • The climate change, which leads to a meltdown of permafrost and sea ice, and the increase in drilling and mining in the Arctic could expose us to dangerous historical viruses, which survived under the surface.
  • Corona could have taught some of us that panic is not the best reaction and that owning toilet paper for years does not keep anyone save. But solidarity does!

The best news is that in the past mankind survived viruses and bacteria at the end!

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