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How does septicemic plague affect the bloodstream?

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two plague victims with sores lying in bed, while a robed figure gestures above them. — plague Image depicting victims of the sixth biblical plague.

In septicemic plague, the bloodstream is extensively invaded by the bacterium Yersinia, leading to a condition known as septicemia, or blood poisoning. This invasion can occur directly from a flea bite or as a complication of bubonic plague.12

Once the bacteria enter the bloodstream, they multiply rapidly, causing systemic symptoms such as fatigue, fever, and internal bleeding. The presence of these bacteria in the blood triggers a severe immune response, which can result in widespread coagulation within the blood vessels, potentially reducing blood flow to vital organs and tissues.23

Because the infection spreads so aggressively through the circulatory system, septicemic plague is extremely dangerous; in untreated cases, it can lead to death before other forms of the disease, such as bubonic or pneumonic plague, have time to manifest. Prompt medical intervention with antibiotics is essential to prevent the progression to septic shock, which carries a high mortality rate.123