The History of Pandemics
Pan·dem·ic /panˈdemik/ (of a disease) prevalent over a whole country or the world.
As humans have spread across the world, so have infectious diseases. Even in this modern era, outbreaks are nearly constant, though not every outbreak reaches pandemic level as COVID-19 has.
Today’s visualization outlines some of history’s most deadly pandemics, from the Antonine Plague to the current COVID-19 event.
A Timeline of Historical Pandemics
Disease and illnesses have plagued humanity since the earliest days, our mortal flaw. However, it was not until the marked shift to agrarian communities that the scale and spread of these diseases increased dramatically.
Widespread trade created new opportunities for human and animal interactions that sped up such epidemics. Malaria, tuberculosis, leprosy, influenza, smallpox, and others first appeared during these early years.
The more civilized humans became – with larger cities, more exotic trade routes, and increased contact with different populations of people, animals, and ecosystems – the more likely pandemics would occur.
Here are some of the major pandemics that have occurred over time:
|Name||Time period||Type / Pre-human host||Death toll|
|Antonine Plague||165-180||Believed to be either smallpox or measles||5M|
|Japanese smallpox epidemic||735-737||Variola major virus||1M|
|Plague of Justinian||541-542||Yersinia pestis bacteria / Rats, fleas||30-50M|
|Black Death||1347-1351||Yersinia pestis bacteria / Rats, fleas||200M|
|New World Smallpox Outbreak||1520 – onwards||Variola major virus||56M|
|Great Plague of London||1665||Yersinia pestis bacteria / Rats, fleas||100,000|
|Italian plague||1629-1631||Yersinia pestis bacteria / Rats, fleas||1M|
|Cholera Pandemics 1-6||1817-1923||V. cholerae bacteria||1M+|
|Third Plague||1885||Yersinia pestis bacteria / Rats, fleas||12M (China and India)|
|Yellow Fever||Late 1800s||Virus / Mosquitoes||100,000-150,000 (U.S.)|
|Russian Flu||1889-1890||Believed to be H2N2 (avian origin)||1M|
|Spanish Flu||1918-1919||H1N1 virus / Pigs||40-50M|
|Asian Flu||1957-1958||H2N2 virus||1.1M|
|Hong Kong Flu||1968-1970||H3N2 virus||1M|
|HIV/AIDS||1981-present||Virus / Chimpanzees||25-35M|
|Swine Flu||2009-2010||H1N1 virus / Pigs||200,000|
|SARS||2002-2003||Coronavirus / Bats, Civets||770|
|Ebola||2014-2016||Ebolavirus / Wild animals||11,000|
|MERS||2015-Present||Coronavirus / Bats, camels||850|
|COVID-19||2019-Present||Coronavirus – Unknown (possibly pangolins)||6.6M (Johns Hopkins University estimate as of October 19, 2022)|
Despite the persistence of disease and pandemics throughout history, there’s one consistent trend over time – a gradual reduction in the death rate. Healthcare improvements and understanding the factors that incubate pandemics have been powerful tools in mitigating their impact.
October 19, 2022 Update: Due to popular request, we’ve also visualized how the death tolls of each pandemic stack up as a share of total estimated global populations at the time.
Wrath of the Gods
In many ancient societies, people believed that spirits and gods inflicted disease and destruction upon those that deserved their wrath. This unscientific perception often led to disastrous responses that resulted in the deaths of thousands, if not millions.
In the case of Justinian’s plague, the Byzantine historian Procopius of Caesarea traced the origins of the plague (the Yersinia pestis bacteria) to China and northeast India, via land and sea trade routes to Egypt where it entered the Byzantine Empire through Mediterranean ports.
Despite his apparent knowledge of the role geography and trade played in this spread, Procopius laid blame for the outbreak on the Emperor Justinian, declaring him to be either a devil, or invoking God’s punishment for his evil ways. Some historians found that this event could have dashed Emperor Justinian’s efforts to reunite the Western and Eastern remnants of the Roman Empire, and marked the beginning of the Dark Ages.
Luckily, humanity’s understanding of the causes of disease has improved, and this is resulting in a drastic improvement in the response to modern pandemics, albeit slow and incomplete.
The practice of quarantine began during the 14th century, in an effort to protect coastal cities from plague epidemics. Cautious port authorities required ships arriving in Venice from infected ports to sit at anchor for 40 days before landing — the origin of the word quarantine from the Italian “quaranta giorni”, or 40 days.
One of the first instances of relying on geography and statistical analysis was in mid-19th century London, during a cholera outbreak. In 1854, Dr. John Snow came to the conclusion that cholera was spreading via tainted water and decided to display neighborhood mortality data directly on a map. This method revealed a cluster of cases around a specific pump from which people were drawing their water from.
While the interactions created through trade and urban life play a pivotal role, it is also the virulent nature of particular diseases that indicate the trajectory of a pandemic.
Scientists use a basic measure to track the infectiousness of a disease called the reproduction number — also known as R0 or “R naught.” This number tells us how many susceptible people, on average, each sick person will in turn infect.
Measles tops the list, being the most contagious with a R0 range of 12-18. This means a single person can infect, on average, 12 to 18 people in an unvaccinated population.
While measles may be the most virulent, vaccination efforts and herd immunity can curb its spread. The more people are immune to a disease, the less likely it is to proliferate, making vaccinations critical to prevent the resurgence of known and treatable diseases.
It’s hard to calculate and forecast the true impact of COVID-19, as the outbreak is still ongoing and researchers are still learning about this new form of coronavirus.
Urbanization and the Spread of Disease
We arrive at where we began, with rising global connections and interactions as a driving force behind pandemics. From small hunting and gathering tribes to the metropolis, humanity’s reliance on one another has also sparked opportunities for disease to spread.
Urbanization in the developing world is bringing more and more rural residents into denser neighborhoods, while population increases are putting greater pressure on the environment. At the same time, passenger air traffic nearly doubled in the past decade. These macro trends are having a profound impact on the spread of infectious disease.
As organizations and governments around the world ask for citizens to practice social distancing to help reduce the rate of infection, the digital world is allowing people to maintain connections and commerce like never before.
Editor’s Note: The COVID-19 pandemic is in its early stages and it is obviously impossible to predict its future impact. This post and infographic are meant to provide historical context, and we will continue to update it as time goes on to maintain its accuracy.
Update (October 19, 2022): We’ve adjusted the death toll for COVID-19, and will continue to update on a regular basis.
Charted: Healthcare Spending and Life Expectancy, by Country
This graphic looks at average life expectancies in countries around the world, compared to each country’s healthcare spending per capita.
Charted: Healthcare Spending and Life Expectancy, by Country
Over the last century, life expectancy at birth has more than doubled across the globe, largely thanks to innovations and discoveries in various medical fields around sanitation, vaccines, and preventative healthcare.
Yet, while the average life expectancy for humans has increased significantly on a global scale, there’s still a noticeable gap in average life expectancies between different countries.
What’s the explanation for this divide? According to World Bank data compiled by Truman Du, it may be partially related to the amount of money a country spends on its healthcare.
More Spending Generally Means More Years
The latest available data from the World Bank includes both the healthcare spending per capita of 178 different countries and their average life expectancy.
Perhaps unsurprisingly, the analysis found that countries that spent more on healthcare tended to have higher average life expectancies up until reaching the 80-year mark.
|Country||Health expenditure per capita (USD, 2019)||Life expectancy at birth, total (years, 2020)|
|United Arab Emirates||$1,843||78|
|Bosnia and Herzegovina||$554||78|
|Antigua and Barbuda||$760||77|
|Iran, Islamic Rep.||$470||77|
|Trinidad and Tobago||$1,168||74|
|St. Vincent and the Grenadines||$355||73|
|Egypt, Arab Rep.||$150||72|
|Sao Tome and Principe||$108||71|
|Papua New Guinea||$65||65|
|Congo, Dem. Rep.||$21||61|
However, there were a few slight exceptions. For instance, while the United States has the largest spending of any country included in the dataset, its average life expectancy of 77 years is lower than many other countries that spend far less per capita.
What’s going on in the United States? While there are several intermingling factors at play, some researchers believe a big contributor is the country’s higher infant mortality rate, along with its higher relative rate of violence among young adults.
On the other end of the spectrum, Japan, Singapore, and South Korea have the highest life expectancies on the list despite their relatively low spending per capita.
It’s worth mentioning that this wasn’t always the case—in the 1960s, Japan’s life expectancy was actually the lowest among the G7 countries, and South Korea’s was below 60 years, making it one of the top 30 countries by improved life expectancy:
View the full-size infographic
In fact, the last 60 years have seen many countries substantially increase their average life expectancies from the 30-40 year range to 70+ years. But as the header chart shows, there are still many countries lagging behind in Africa, Asia, and Oceania.
How High Can Average Life Expectancy Go?
Since people are living longer than they’ve ever lived before, how much higher will average life expectancies be in another 100 years?
Recent research published in Nature Communications suggests that, under the right circumstances, human beings have the potential to live up to 150 years.
Projections from the UN predict that growth will be divided, with developed countries seeing higher life expectancies than developing regions.
However, as seen in the above chart from the World Economic Forum and using UN data, it’s likely the gap between developed and developing countries will narrow over time.
Visualizing the Composition of Blood
Despite its simple appearance, blood is made up of many microscopic elements. This infographic visualizes the composition of blood.
The Composition of Blood
Have you ever wondered what blood is made up of?
With the average adult possessing five to six liters of blood in the body, this fluid is vital to our lives, circulating oxygen through the body and serving many different functions.
Despite its simple, deep-red appearance, blood is comprised of many tiny chemical components. This infographic visualizes the composition of blood and the microscopic contents in it.
What is Blood Made Up Of?
There are two main components that comprise blood:
- Plasma – 55%
Plasma is the fluid or aqueous part of blood, making up more than half of blood content.
- Formed elements – 45%
Formed elements refer to the cells, platelets, and cell fragments that are suspended in the plasma.
Plasma is primarily made up of water (91%), salts, and enzymes, but it also carries important proteins and components that serve many bodily functions.
Plasma proteins make up 7% of plasma contents and are created in the liver. These include:
These proteins keep fluids from leaking out of blood vessels into other parts of the body. They also transport important molecules like calcium and help neutralize toxins.
These play an important role in clotting blood and fighting infections and are also transporters of hormones, minerals, and fats.
- Fibrinogen and Prothrombin
Both of these proteins help stop bleeding by facilitating the creation of blood clots during wound-healing.
Water and proteins make up 98% of plasma in blood. The other 2% is made up of small traces of chemical byproducts and cellular waste, including electrolytes, glucose, and other nutrients.
There are three categories of formed elements in blood: platelets, white blood cells, and red blood cells. Red blood cells make up 99% of formed elements, with the other 1% comprised of platelets and white blood cells.
- Platelets (Thrombocytes)
Platelets are cells from the immune system with the primary function of forming clots to reduce bleeding from wounds. This makes them critical not only for small wounds like cuts but also for surgeries and traumatic injuries.
- White blood cells (Leukocytes)
White blood cells protect our bodies from infection. There are five types of white blood cells with different roles in fighting infections: some attack foreign cells and viruses, some produce antibodies, some clean up dead cells, and some respond to allergens.
- Red blood cells (Erythrocytes)
Red blood cells deliver fresh oxygen and nutrients all over the body. They contain a special protein called hemoglobin, which carries oxygen and gives blood its bright red color.
The lifespan of a typical red blood cell is around 120 days, after which it dies and is replaced by a new cell. Our bodies are constantly producing red blood cells in the bone marrow, at a rate of millions of cells per second.
Abnormal Red Blood Cells
Normal red blood cells are round, flattened disks that are thinner in the middle. However, certain diseases and medical therapies can change the shape of red blood cells in different ways.
Here are the types of abnormal red blood cells and their associated diseases:
Sickle cell anemia is a well-known disease that affects the shape of red blood cells. Unlike normal, round red blood cells, cells associated with sickle cell disease are crescent- or sickle-shaped, which can slow and block blood flow.
Other common causes of abnormally shaped red blood cells are thalassemia, hereditary blood disorders, iron deficiency anemia, and liver disease. Identifying abnormal blood cells plays an important role in diagnosing the underlying causes and in finding treatments.
The Functions of Blood
We know that blood is vital, but what does it actually do in the body?
For starters, here are some of the functions of blood:
- Blood transports oxygen to different parts of the body, providing an energy source. It also delivers carbon dioxide to the lungs for exhalation.
- The platelets, white blood cells, and plasma proteins in blood play an important role in fighting infections and clotting.
- Blood transports the body’s waste products to the kidneys and liver, which filter it and recirculate clean blood.
- Blood helps regulate the body’s internal temperature by absorbing and distributing heat throughout the body.
While we all know that we can’t live without blood, it serves many different functions in the body that we often don’t notice. For humans and many other organisms alike, blood is an integral component that keeps us alive and going.
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