plaga

Plāga in Latin means a blow, a strike, a wound. The word entered Old French as plage and English as 'plague' by the fourteenth century. The timing was not accidental. The Black Death arrived in England in 1348 and killed between a third and half the population. The disease needed a word that conveyed devastation rather than mere illness. 'Plague' — a blow — was the right word for a catastrophe that felt like being struck by God.

The bubonic plague is caused by the bacterium Yersinia pestis, transmitted through flea bites from infected rats. The bacterium was identified in 1894 by Alexandre Yersin in Hong Kong during the Third Pandemic. Three major plague pandemics are recorded: the Plague of Justinian (541-549 CE, ~25 million dead), the Black Death (1347-1351, ~75-200 million dead), and the Third Pandemic (1855-1960, ~12 million dead). Each was a different outbreak of the same bacterium.

The word 'plague' generalized beyond the specific disease. The ten plagues of Egypt in the Book of Exodus. A plague of locusts. 'A plague on both your houses' (Shakespeare, Romeo and Juliet). The word means any devastating affliction — a blow from above, indiscriminate and overwhelming. The disease gave the word its weight, and the word returned the favor.

Yersinia pestis still exists. Prairie dogs in the American West carry it. Cases occur every year. The disease is now treatable with antibiotics if caught early. But the word 'plague' retains its power. No modern disease — not HIV, not COVID-19 — is routinely called a plague in medical literature, because the word is too heavy. It implies apocalypse.