Britannica Sources used in this answer

How did septicemic plague differ from bubonic plague?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Medieval illustration of Brotherhood of the Cross flagellants in robes and pointed hats walking in procession, some carrying a crucifix and banners, during the Black Death. — Black Death Flagellants in the Netherlands scourging themselves in atonement, believing that the Black Death is a punishment from God for their sins, 1349.

While both bubonic and septicemic plague are caused by the bacterium Yersinia pestis, they differ significantly in their clinical presentation and progression.123

Bubonic Plague: This is the most common form of the disease. It is characterized by the infection of the lymphatic system, which leads to the development of painful, swollen lymph nodes known as buboes, typically in the groin, armpits, or neck. Other symptoms include fever, chills, fatigue, and headache.4312
Septicemic Plague: This form occurs when the bloodstream is extensively invaded by the bacteria. It is more severe than the bubonic form and can arise either as a direct result of a flea bite or as a complication of untreated bubonic plague. Its primary symptoms include fever, fatigue, and internal bleeding.1532

Crucially, septicemic plague is so aggressive that in untreated cases, death can occur before the characteristic buboes of bubonic plague or the lung involvement of pneumonic plague have time to manifest.15