Cantonese Woman Wearing a Silk Mask During the Third Bubonic Plague, 1900

Cantonese woman with bound feet wearing a silk mask during the third bubonic plague, 1900.

The third plague pandemic was a major bubonic plague pandemic that began in Yunnan, China, in 1855 during the fifth year of the Xianfeng Emperor of the Qing dynasty. This episode of bubonic plague spread to all inhabited continents, and ultimately led to more than 12 million (perhaps 15 million) deaths in India and China, with about 10 million killed in India alone, making it one of the deadliest pandemics in history. According to the World Health Organization, the pandemic was considered active until 1960, when worldwide casualties dropped to 200 per year. Plague deaths have continued at a lower level for every year since.

The name refers to this pandemic being the third major bubonic plague outbreak to affect European society. The first began with the Plague of Justinian, which ravaged the Byzantine Empire and surrounding areas in 541 and 542; the pandemic persisted in successive waves until the middle of the 8th century. The second began with the Black Death, which killed at least one third of Europe's population in a series of expanding waves of infection from 1346 to 1353; this pandemic recurred regularly until the 19th century.

Casualty patterns indicate that waves of this late-19th-century/early-20th-century pandemic may have come from two different sources. The first was primarily bubonic and was carried around the world through ocean-going trade, through transporting infected persons, rats, and cargoes harboring fleas. The second, more virulent strain, was primarily pneumonic in character with a strong person-to-person contagion. This strain was largely confined to Asia, in particular Manchuria and Mongolia.