De contagione et contagiosis morbis

De contagione et contagiosis morbis (1546) by Girolamo Fracastoro proposed a scientific germ theory of disease, predating empirical formulation by over 300 years. Fracastoro stated that diseases are caused by different, rapidly multiplying minute bodies. These bodies transfer from an infected person to a healthy one through direct contact, contaminated objects like clothing, or the air.1

While ancient scholars like Marcus Varro had suggested imperceptible particles cause disease, Fracastoro's work was the first scientific explanation of contagion, infection, disease germs, and transmission methods. His theory, though influential in his time, was later experimentally validated by scientists like Louis Pasteur and Robert Koch.12