Historic Epidemic and Pandemic Diseases

Diseases that changed history

Epidemics and pandemics have shaped human history as much as wars and empires. They have toppled civilizations, changed economies and inspired major scientific breakthroughs.

The Plague of Justinian (541–549 CE)

The first recorded plague pandemic struck the Byzantine Empire under Emperor Justinian. It may have killed a quarter or more of the population around the Mediterranean and weakened the empire.

The Black Death (1346–1353)

The Black Death was the deadliest pandemic in recorded history.

• Cause: the bacterium Yersinia pestis, carried by fleas on rats, and spread between people through the air in its pneumonic form.
• Spread: along trade routes from Central Asia to the Black Sea, then by ship to Europe.
• Death toll: an estimated 25–50 million people in Europe, roughly one-third to one-half of its population, plus millions more in Asia and Africa.
• Symptoms: painful swollen lymph nodes called buboes, fever and blackened skin.

Effects: labour shortages raised wages for surviving workers and helped end the feudal system. The city of Venice began holding ships for 40 days before passengers could land; the Italian quaranta giorni ("forty days") gave us the word quarantine.

Smallpox

Smallpox was caused by the variola virus. It killed about 30% of people infected and left survivors scarred.

• It killed an estimated 300 million people in the 20th century alone.
• When Europeans arrived in the Americas, they brought smallpox and other diseases. Indigenous peoples had no immunity, and epidemics killed a huge share of the population, devastating many nations.
• In 1796, English doctor Edward Jenner showed that infecting people with mild cowpox protected them from smallpox. This was the first vaccine (from vacca, Latin for "cow").
• A global vaccination campaign led by the WHO achieved eradication. The last natural case was in Somalia in 1977, and smallpox was declared eradicated in 1980, the first human disease ever wiped out.

Cholera (1800s–today)

Cholera is a bacterial infection spread by water contaminated with sewage. It causes severe diarrhea and can kill within hours.

• Seven cholera pandemics have occurred since 1817.
• In 1854, London doctor John Snow mapped cholera deaths and traced them to one water pump on Broad Street. When the pump handle was removed, cases dropped. This helped found the science of epidemiology.
• Clean water and sewer systems largely ended cholera in wealthy countries, but it still affects places without safe water.

The 1918 influenza pandemic ("Spanish flu")

• The Spanish flu infected about one-third of the world’s population.
• It killed an estimated 50 million people, more than World War I.
• Unusually, it killed many healthy young adults.
• In Canada, about 50 000 people died.
• It was called "Spanish" only because Spain, neutral in the war, reported on it openly.

Responses included closing schools, banning gatherings and wearing masks. The pandemic led to the creation of Canada’s federal Department of Health in 1919.

Tuberculosis

Tuberculosis (TB), a bacterial lung disease, has killed more people over history than almost any other disease. In the 1800s it was called "consumption." Sanatoriums, vaccines and antibiotics greatly reduced it in Canada, but rates remain much higher in some Inuit communities. TB is still one of the world’s leading infectious killers.

Polio

Polio is a viral disease that can cause paralysis. Epidemics in the 1940s and 1950s frightened parents across North America. Jonas Salk’s vaccine (1955) and Albert Sabin’s oral vaccine (1960s) led to its elimination from Canada and most of the world.

HIV/AIDS

HIV, identified in the early 1980s, attacks the immune system and causes AIDS. It has caused about 40 million deaths. Since the 1990s, antiretroviral medicines have turned HIV from a death sentence into a manageable condition for those who can get treatment.

COVID-19

The COVID-19 pandemic, declared in 2020, caused millions of deaths worldwide, closed schools and businesses, and led to the fastest vaccine development in history.

Summary table

Lessons learned

• Clean water and sanitation prevent many diseases.
• Vaccines can control and even eradicate diseases.
• Early detection and international cooperation slow spread.
• Diseases often hit poor and marginalized communities hardest.

Common mistakes

• Thinking the Black Death was caused by rats alone. Fleas spread it, and it also spread person to person.
• Thinking the 1918 flu started in Spain. Its origin is uncertain.

Try it yourself

1. Make a timeline of five pandemics with their causes and effects.
2. Recreate John Snow’s map: plot "cases" on a grid of streets and find the source.
3. Research how one pandemic affected Indigenous communities in Canada.

Quick recap

• Pandemics have killed millions and changed societies.
• The Black Death killed up to half of Europe and gave us the word quarantine.
• Smallpox was the first disease eradicated, thanks to vaccines.
• John Snow’s work on cholera founded epidemiology.
• Clean water, vaccines and public health have tamed many diseases.