A visual history of pandemics
15 Mar 2020
Nicolas LePan
Mining Editor,
Visual Capitalist
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 the Novel Coronavirus (COVID-19) has.
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:
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.
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.
Importing
Disease
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.
Tracking
Infectiousness
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.
A chart
showing how many people each disease will 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.
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