Disease & Contagion
From imbalanced humors to sequenced pathogens — the long hunt for what makes us ill.
Each star is a thinker or work; solid lines draw the constellation of a school, dashed threads the passage of ideas between eras.
Select any point on the timeline to read about it.
All entries by era
Disease & Contagion 450 BCE – 2030 CE
From imbalanced humors to sequenced pathogens — the long hunt for what makes us ill.
- 400 BCE
Hippocratic corpus. The Hippocratic writers reject supernatural causes and root illness in an imbalance of four bodily fluids — blood, phlegm, black and yellow bile. However mistaken, the theory made disease natural and treatable, and its emphasis on observation founded clinical medicine.
- 170 CE
Galen of Pergamon. Galen builds humoral theory into a vast, internally consistent system of anatomy, physiology and therapy. His authority becomes so complete that for over a millennium European and Islamic medicine largely refines Galen rather than questioning him.
- 1546 CE
Girolamo Fracastoro, De contagione. Fracastoro proposes that specific diseases spread by tiny 'seeds' (seminaria) passing between people, objects and the air. Centuries before microbes could be seen, he articulates a strikingly modern idea of transmissible, disease-specific agents.
- 1676 CE
Antonie van Leeuwenhoek, microscopy. With hand-ground lenses, Leeuwenhoek becomes the first to see bacteria and protozoa, a teeming microscopic world he calls 'animalcules'. He did not link them to disease, but he revealed the very organisms that germ theory would one day indict.
- 1796 CE
Edward Jenner, smallpox vaccination. Noticing that milkmaids who caught cowpox were spared smallpox, Jenner deliberately inoculates a boy with cowpox and shows it confers protection. Without knowing the mechanism, he founds immunisation — the tool that would eventually eradicate smallpox entirely.
- 1854 CE
John Snow, Broad Street pump. During a London cholera outbreak, Snow maps cases and traces them to a single contaminated water pump, removing its handle to stop the spread. His shoe-leather epidemiology undercuts the reigning 'miasma' theory of bad air and shows disease can travel by water.
- 1861 CE
Louis Pasteur, germ theory. Pasteur's experiments disprove spontaneous generation and demonstrate that microorganisms cause fermentation, spoilage and disease. Germ theory replaces miasma for good and gives medicine, surgery and public health a firm causal foundation.
- 1882 CE
Robert Koch, tubercle bacillus. Koch isolates the bacterium that causes tuberculosis and formalises rigorous criteria — Koch's postulates — for proving that a particular microbe causes a particular disease. Bacteriology becomes an exact science, and pathogens are identified one by one.
- 1928 CE
Alexander Fleming, penicillin. Fleming notices that a stray mould kills the bacteria around it, discovering penicillin. Developed into a drug in the 1940s, it and the antibiotics that followed turn once-fatal infections into curable conditions — one of the greatest advances in the history of medicine.
- 1983 CE
Montagnier & Barré-Sinoussi, HIV. The identification of HIV as the cause of AIDS confronts modern medicine with a lethal, previously unknown pandemic virus. It spurs decades of virology and drug development, and reminds a confident age that new pathogens can still emerge and spread worldwide.
- 2003 CE
Genomic epidemiology (SARS onward). During the 2003 SARS outbreak the culprit coronavirus is sequenced within weeks, and rapid genomics becomes a frontline tool for tracing how pathogens spread and mutate. Disease surveillance shifts from symptoms and case maps to reading the genome of the enemy in real time.
- 2020 CE
COVID-19 & mRNA vaccines. When SARS-CoV-2 emerges, its genome is shared within days and mRNA vaccines are designed almost immediately, then rolled out within a year. The pandemic fuses genomics, immunology and global logistics — and shows both the power and the fragility of modern disease control.
The milestones
c. 400 BCE
Hippocratic corpus
The four humors
The Hippocratic writers reject supernatural causes and root illness in an imbalance of four bodily fluids — blood, phlegm, black and yellow bile. However mistaken, the theory made disease natural and treatable, and its emphasis on observation founded clinical medicine.
c. 170 CE
Galen of Pergamon
Humoralism systematised
Galen builds humoral theory into a vast, internally consistent system of anatomy, physiology and therapy. His authority becomes so complete that for over a millennium European and Islamic medicine largely refines Galen rather than questioning him.
1546
Girolamo Fracastoro, De contagione
Seeds of contagion
Fracastoro proposes that specific diseases spread by tiny 'seeds' (seminaria) passing between people, objects and the air. Centuries before microbes could be seen, he articulates a strikingly modern idea of transmissible, disease-specific agents.
1676
Antonie van Leeuwenhoek, microscopy
A world of 'animalcules'
With hand-ground lenses, Leeuwenhoek becomes the first to see bacteria and protozoa, a teeming microscopic world he calls 'animalcules'. He did not link them to disease, but he revealed the very organisms that germ theory would one day indict.
1796
Edward Jenner, smallpox vaccination
The first vaccine
Noticing that milkmaids who caught cowpox were spared smallpox, Jenner deliberately inoculates a boy with cowpox and shows it confers protection. Without knowing the mechanism, he founds immunisation — the tool that would eventually eradicate smallpox entirely.
1854
John Snow, Broad Street pump
Disease mapped to water
During a London cholera outbreak, Snow maps cases and traces them to a single contaminated water pump, removing its handle to stop the spread. His shoe-leather epidemiology undercuts the reigning 'miasma' theory of bad air and shows disease can travel by water.
1861
Louis Pasteur, germ theory
Microbes cause disease
Pasteur's experiments disprove spontaneous generation and demonstrate that microorganisms cause fermentation, spoilage and disease. Germ theory replaces miasma for good and gives medicine, surgery and public health a firm causal foundation.
1882
Robert Koch, tubercle bacillus
Proving a specific cause
Koch isolates the bacterium that causes tuberculosis and formalises rigorous criteria — Koch's postulates — for proving that a particular microbe causes a particular disease. Bacteriology becomes an exact science, and pathogens are identified one by one.
1928
Alexander Fleming, penicillin
The antibiotic age
Fleming notices that a stray mould kills the bacteria around it, discovering penicillin. Developed into a drug in the 1940s, it and the antibiotics that followed turn once-fatal infections into curable conditions — one of the greatest advances in the history of medicine.
1983
Montagnier & Barré-Sinoussi, HIV
A new virus, a new fear
The identification of HIV as the cause of AIDS confronts modern medicine with a lethal, previously unknown pandemic virus. It spurs decades of virology and drug development, and reminds a confident age that new pathogens can still emerge and spread worldwide.
2003
Genomic epidemiology (SARS onward)
Tracking outbreaks by sequence
During the 2003 SARS outbreak the culprit coronavirus is sequenced within weeks, and rapid genomics becomes a frontline tool for tracing how pathogens spread and mutate. Disease surveillance shifts from symptoms and case maps to reading the genome of the enemy in real time.
2020 →
COVID-19 & mRNA vaccines
From sequence to vaccine in days
When SARS-CoV-2 emerges, its genome is shared within days and mRNA vaccines are designed almost immediately, then rolled out within a year. The pandemic fuses genomics, immunology and global logistics — and shows both the power and the fragility of modern disease control.