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The History of the Black Death and How a Medieval Pandemic Still Affects Us Today

  • Writer: FibonacciMD
    FibonacciMD
  • 21 hours ago
  • 8 min read

Plague doctors from Italy (left) and France (right)
Plague doctors from Italy (left) and France (right)

The Black Death, or plague, was one of the worst pandemics in human history.  Beginning in the 14th century,  it is estimated to have killed at least one-third of Europe’s population or more than 25 million people.  Caused by the bacterium Yersinia pestis, the plague profoundly changed human history.


History of the Black Death 

Plague has been around for thousands of years, with DNA of Yersinia pestis being found in the teeth of skeletons from Siberia dating back about 5,500 years ago.  A separate, later Bronze Age strain, which is directly ancestral to the one that caused the Black Death,  has also been confirmed in remains from approximately 3,800 years ago. 


Historians identify three separate pandemics.  The first, known as the Justinian plague, is thought to have originated in Central Asia, although its exact origin remains debated.    It reached Constantinople in 541 CE, before spreading throughout Europe, North Africa,  and Asia for the next 200 years.


The second pandemic, known as the Black Death, reached Sicily in 1347, likely transported from Asia aboard merchant ships carrying infected rodents and fleas.  From there it swept across Europe, aided by crowded cities, poor sanitation, large rat populations, and extensive trade routes creating ideal conditions for rapid transmission.


It is estimated that between 1347 and 1352, more than 25 million Europeans died from the disease.  The pandemic subsided for a time at the end of the 14th century, but outbreaks recurred in Europe over the next 400 years.  The continued outbreaks still took a serious toll, with at least half of the population of Genoa and Naples dying in the 1656-1657 outbreak, and 2.5 million deaths in France between 1600 and 1670.  Tens of thousands more died in repeated outbreaks in other European cities.  The plague toll was so severe that the population of Western Europe did not recover to pre-1347 levels until the 16th century. 

The third plague pandemic began in China around 1855 and spread via steamship trade routes to the Americas, Australia, and other parts of Asia in the late 1800s and early 1900s.  India was especially hard hit, with an estimated 12 million deaths from the late 1800s to the early 1900s.


Historical Beliefs and Public Health Measures 

Ancient physicians such as Hippocrates (460-370 BCE) and Galen (129-210 CE) promoted the miasma theory, which held that "bad air" caused disease.  That concept shaped medical practice and doctors in the 17th century wore distinctive bird-like protective masks during plague epidemics.  The beak of the mask was filled with aromatic herbs, flowers, spices, and other fragrant materials in an attempt to protect themselves from the “bad air” or miasma.  A plague doctor would inspect suspected cases and then isolate the patients and their families in their homes.

 

The same theory caused authorities in some cities to close public baths, believing warm water opened the skin's pores and allowed miasma to enter the body.  Victims’ clothes and possessions were burned in an attempt to prevent further transmission.  Dedicated plague hospitals were built in Europe to isolate the sick.  Port cities started imposing a 30-day isolation period, which was later extended to 40 days in several Italian ports.  The term quarantine derives from the Italian quaranta giorni, meaning "forty days."


How the Black Death Affected Society

The sheer number of people falling ill and dying reshaped 14th-century society.  The plague led to shortages of farm workers and skilled craftsmen, which caused many feudal landowners to go bankrupt.  The shrinking labor force forced them to pay wages to workers instead of simply providing room and board.  This improved the lot of peasants and artisans and opened new paths to social mobility.


The pandemic also cost the Italian states much of their former power and international standing.

Life in this period was undoubtedly frightening for those who lived through it.  Previously healthy people became ill in massive numbers, and entire towns were abandoned after survivors fled from the infected.  Social structures broke down.  Many priests died, and those that survived frequently refused to administer last rites out of fear of infection.  This fear led to scapegoating with some Europeans blaming Jewish communities for poisoning wells and spreading the plague, sparking antisemitic pogroms in which Jews were killed or beaten.


The Flagellant movement grew in popularity during the Black Death, as many turned to extreme religious movements.  A common belief at the time was that the pandemic was a divine punishment for sin, and the Flagellants believed that self-flagellation or whipping themselves with knotted cords, sometimes embedded with metal tips, was a way to seek absolution.  They also came to believe their presence alone could heal the sick.  During the Black Death, it was difficult for peasants to access a priest, and the Flagellants often filled that gap.  In 1349, Pope Clement VI ordered the suppression of the Flagellant movement because of their increasingly heretical beliefs.


The Plague

Yersinia pestis is the bacterium that causes plague.  It is spread by infected fleas that feed on rodents, most commonly black rats in urban settings. The fleas infect the rats, which in turn infect more feeding fleas.  In Xenopsylla cheopis (the Oriental rat flea), Yersinia pestis blocks the flea's digestive tract, forcing the starving insect to repeatedly bite and regurgitate bacteria into new hosts.


Humans can become infected by getting bitten by infected fleas, direct contact with sick or dead animals, or inhaling infectious respiratory  droplets expelled from a human or animal with pneumonic plague.  Black rats live near humans, and when the rats die, the fleas can readily transfer to human hosts.  Fleas can travel on clothing or bedding, carrying the disease to new locations. 


Axillary buboes in bubonic plague
Axillary buboes in bubonic plague

There are three forms of plague: bubonic, pneumonic, and septicemic.


Bubonic plague, the most common form, presents three to seven days after exposure with high fever, headaches, abdominal and limb pain.  The bacteria multiply in the lymph nodes near the flea bite, causing pus-filled, painful swellings called buboes.


Septicemic plague is rarer, accounting for approximately 10-15% of cases where the bacteria invade the bloodstream, reproduce, and cause an overwhelming systemic infection.


Pneumonic plague is the least common form and causes a rapidly progressive, severe pneumonia.  It can be spread by infected humans through respiratory droplets released by coughing, or less commonly through infected animals.


Discovery of the Cause

In 1894, during a Hong Kong outbreak, Alexandre Yersin from the Pasteur Institute identified the causative bacterium which was later named Yersinia pestis in his honor.  Four years later, French physician Paul-Louis Simond demonstrated that fleas from infected rats could transmit the disease to healthy rats.  In 1927, Ricardo Jorge, a Portuguese physician, expanded understanding of the disease when he reported that wild rodents, including gerbils, squirrels, and marmots, can also serve as long-term plague reservoirs.


Plague in the Modern Era

In the United States, an average of about seven cases of plague are reported each year, while globally several hundred to a few thousand cases occur annually.  Prior to the introduction of antibiotics, plague was frequently fatal, with an overall mortality rate of approximately 66% among reported U.S. cases.  Mortality was considerably higher for the septicemic and pneumonic forms than for the bubonic form.  Modern antibiotic therapy has reduced overall mortality to approximately 11%.


Early treatment with antibiotics can prevent progression of the disease.  Close contacts may also be given prophylactic antibiotics to prevent disease.  Recommended antibiotics include streptomycin, gentamicin, fluoroquinolones, doxycycline, and chloramphenicol.


There has been a search for a plague vaccine, not only to prevent natural disease, but also to combat the potential bioweaponization of pneumonic plague.  During the 1990s, a plague vaccine was marketed but was discontinued in 1999 due to both severe side effects, and because it only had limited protection against pneumonic plague.  In 2026, scientists published their findings that two experimental vaccines they developed provided 80%-100% protection against pneumonic plague in mice, which is a promising advance.


Genetic Legacy 

It is postulated that the large number of deaths during the Black Death drove natural selection for individuals with genotypes that offered some immunity to the disease.  Researchers have since found that the same gene that confers protection from plague (ERAP2) may increase susceptibility of descendants to Crohn’s disease and possibly to rheumatoid arthritis.  It appears that an evolutionary advantage that saved lives during the Black Death may also be a health risk for some of their modern descendants.


Summary: The Lasting Impact of the Black Death

The Black Death terrorized people living in the Middle Ages, causing millions of deaths across multiple episodes that stretched over hundreds of years.  It changed society by reshaping labor compensation, class mobility, religious life, the power of nations, and helped establish the concepts of isolation and quarantine.  For centuries it was thought that bad air, or miasma, was the cause and it was not until the late 1800s that the actual etiology of the plague was identified.  The advent of effective antibiotics and better infection control measures has reduced the number of deadly infections.  Fears that pneumonic plague could be used as a bioweapon, have spurred research into finding an effective vaccine.  Promisingly, in 2026,  two experimental vaccines were successfully tested in mice.  


f you liked this article, you may also enjoy reading about another plague where people danced for days, The Dancing Plague of 1518

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