Contagia
Contagia is a term that appears in historical and linguistic contexts to refer to contagious agents or to contagion itself. It derives from the Latin noun contagium (“a substance capable of producing disease”). In Latin, the neuter plural is contagia, a form that has been borrowed into some medical and philosophical writings. In English-language medical literature, the standard term for the phenomenon is contagion, with the plural contagions; contagia is mainly encountered in older texts or discussions of etymology.
Historically, contagia was used to describe whatever agents or substances were believed to transmit disease, including
Modern usage and context have shifted with the rise of germ theory. From the 19th century onward,
See also: contagion, contagium, pathogen, infectious disease, transmission.