Around the year 9000 BC, man gradually evolves from a hunter-gatherer lifestyle
to a relatively more sedentary one.
In Mesopotamia, initially, man begins to develop agriculture and livestock.
This new proximity between animals and man facilitates the transmission of diseases to the latter.
Food production increases; communities, villages and cities grow; trade routes appear;
and the first wars take place.
All this contributes to the spread of new contagious diseases.
Although there aren’t enough historical traces or documentation,
the first epidemics probably take place at this time and perhaps even the first pandemics,
i.e. the spread of an epidemic among different people over large geographical areas.
Some religious texts and Egyptian papyri recount the first outbreaks.
The development of writing allows a Greek historian to document a pandemic around 430 BC.
Known as the Plague of Athens, it is a disease that remains unidentified to this day.
According to the story, and thus the Greek point of view, the illness emerges in Ethiopia,
spreads in Egypt, Libya, and then throughout the Mediterranean basin.
Athens is at war with Sparta and its allies.
The city hosts many refugees and is under siege.
Too densely populated and in poor hygienic conditions, the Plague of Athens worsens
and kills 25-30% of the population, which facilitates Spartan victory.
Around the year 165, when the Mediterranean basin is dominated by the Roman Empire,
the Antonine Plague appears, which is probably a smallpox pandemic.
It starts in Mesopotamia and spreads rapidly westward following military travel patterns.
The disease kills 5 million people out of the then global population of 200 to 250 million people.
The Roman Empire is hit hard.
Other epidemics further weaken it over the following centuries,
probably influencing the fall of the Western Roman Empire.
In 541 begins the first known pandemic of bubonic plague,
linked to a bacteria infecting small mammals, mainly rats, and their fleas.
In some cases, the rat fleas bite humans and transmit bacteria to them.
Once the infection reaches the lungs, it becomes highly contagious between humans.
According to recent studies, the Plague of Justinian started in Central Asia
and spread via land and sea trade routes to the Byzantine Empire.
The capital Constantinople is badly affected.
As it lies on a commercial crossroad, the disease spreads throughout the Mediterranean basin.
Byzantine military troops engaged in the West are contaminated, which halts the expansion of the empire.
In Rome, Pope Pelagius II succumbs to the disease.
In Mesopotamia, the Byzantine and Sasanian empires,
already severely affected by the pandemic, lose steam in war.
This benefits the Arabs who start their Muslim conquests.
The Sasanian Empire collapses while the Byzantine Empire is greatly reduced.
The Plague of Justinian claims between 30 and 100 million victims over two centuries.
Leprosy is a bacterial disease mentioned in texts dating back to Antiquity.
Probably native to East Africa according to recent studies,
it spreads through Egypt to Asia and Europe following trade routes.
As Europe’s population gets denser, it is likely that crusades to Jerusalem
accelerated the spread of leprosy on the continent.
Bad hygiene, lack of sewers and poorly ventilated homes fosters transmission of this disease,
which is otherwise not very contagious.
The poor are the worst affected.
Exclusion measures are taken against the sick.
Lepers are considered already dead by the Catholic religion.
They are isolated in leper colonies, which can be anything
from a simple hut on the edge of a village or leprosaria - sickroom facilities - in cities.
Lepers end their lives in such confinements, completely isolated from the outside world.
The Black Death is considered the second pandemic of bubonic plague.
It originates in the steppes of Central Asia, and spreads across the continent.
On the shores of the Black Sea, warriors of the Golden Horde besiege the Genoese city of Caffa.
Weakened by the plague, they catapult their dead into the city to spread the disease.
Rats also likely further contaminate the city.
After the siege fails, Genoese sailors resume trade across Europe, spreading the plague in port cities.
The disease then spreads inland.
Only regions of Poland, Bohemia and Hungary are spared.
The plague manifests strongly in densely populated areas and disproportionately affects the poor,
the malnourished and those living in unsanitary conditions.
Doctors are overwhelmed.
In a few years, the disease kills 200 million people worldwide,
a little less than half the European population.
The continent would take two centuries to recover its pre-pandemic demography.
The Black Death is endemic, that is, it would locally resurface several times over the following centuries.
Preventive measures are taken, especially in Venice where ships have to wait 40 days
before being able to enter the port.
These are the first quarantines -- quaranta being the Italian word for the number 40.
In Europe, the construction of new, more efficient vessels
allows the Spanish and Portuguese to broaden exploration.
With Christopher Columbus landing in America, and Vasco da Gama opening a sea route to India
through the African coasts, exchanges rapidly increase between people
previously isolated from each other and with different immunity systems.
People from the Old World import along with them a dozen diseases still unknown in the New World.
Smallpox proves particularly devastating for Native Americans.
Epidemics decimate entire populations even before the arrival of European settlers.
Conversely, a form of virulent syphilis, a sexually transmitted infection,
is imported from America to Europe.
Furthermore, tropical diseases such as yellow fever and malaria,
caused by parasites, spread around the world via carrier mosquitoes that accompany ships.
Meanwhile, medicine continues to evolve in the face of multiple disease outbreaks.
In 1768, an English apothecary named John Fewster finds that people infected with cowpox,
a disease dangerous to bovines but not humans, are protected from the smallpox virus.
A few years later, the cowpox vaccine is injected into populations to counter smallpox:
resulting in the first form of vaccine.
The treatment would evolve and the smallpox disease would be eradicated over two centuries.
Cholera is a bacterial infection that only affects the human species
through the ingestion of contaminated food or water.
The disease causes severe diarrhea resulting in life-threatening dehydration.
Without treatment, half of those infected die within a few hours or days.
The disease spreads more rapidly in densely populated areas with poor hygienic conditions.
The first cholera pandemic begins in 1817 in the vicinity of Bengal and spreads in Asia,
Africa and to the gates of Europe.
Five other cholera pandemics would break out over the following century and affect the entire world.
In 1855, in the west of Yunnan, China, begins the third and last pandemic of bubonic plague.
It spreads slowly to the port city of Hong Kong from where, in a few years,
it spreads from ships in ports around the whole world.
But this time, French biologists and doctors discover the bacteria responsible
for the disease and how rat fleas propagate it.
A serum is created and rat extermination measures are taken on vessels which limits numbers,
mainly in developed countries.
British India is still badly affected with around 10 million deaths, while China has 2 million victims.
Influenza is an infectious disease that is difficult to contain
because it is caused by four different strains of viruses that can quickly mutate and generate new epidemics.
The first major flu pandemic, called the Russian flu, raged in 1889 and 1890
from the Eurasian steppes to the European and American continents.
But it’s the second major influenza outbreak, known as the Spanish flu,
which proves to be the most devastating flu pandemic.
Its origins still unknown, it appears during World War I.
In the United States, the virus mutates and becomes virulent.
Transported by soldiers to Europe, the disease spreads through the globe as soon as World War I ends.
A third of the world's population is infected, and about 50 million people die from it.
There would be 2 further flu pandemics causing approximately 1 million deaths each:
the so-called Asian Flu in 1957 and the Hong Kong pandemic in 1968.
Originally from central Africa,
the AIDS virus spreads from chimpanzees to man due to hunting some 60 years earlier.
The virus slowly reaches Leopoldville in the Belgian Congo
from where it spreads across river routes and railways all around the country,
and then across the continent.
In 1964, the return of contaminated Haitian workers takes the disease to North America,
especially in the United States from 1970.
In 1983, in Paris, the Pasteur Institute identifies the HIV virus that causes AIDS,
the disease that weakens the immune system and therefore facilitates the development of other infections.
AIDS then infects people worldwide to qualify as a pandemic in 2005.
Prevention, treatment and contraceptives help curb the disease,
but still results in about 30 million victims in 30 years.
Today, some 40 million people live with HIV.
At the end of 2019, the SARS-CoV-2 virus is probably transmitted from animals to humans
and is first observed in Wuhan, China.
With high levels of globalization, the new disease COVID-19 spreads rapidly around the world.
On March 11, 2020, the World Health Organization declares it a pandemic.
Furthermore, despite major advances in medicine, other diseases still claim many victims.
Plague is still rampant and reappears regularly,
the last epidemic in 2017 hitting Madagascar and Seychelles.
A seventh cholera pandemic has been underway since 1961
and still causes 100,000 global victims each year, according to WHO.
There are under 3 million leprosy patients worldwide,
while seasonal flu kills about 500,000 people annually.
Malaria claims as many victims each year, the vast majority being young children in Sub-Saharan Africa.
Poor and remote populations remain the main victims of these epidemics and pandemics.