[citation needed] It is important to note that septicemic plague may be asymptomatic and may cause death absent of any symptoms.

When rats that carried the plague died of the disease, then the fleas that were using those rodents as a food source must quickly seek a different blood stream, making things very problematic for any human nearby.

These masses don't allow for blood to be processed properly, leaving the flea feeling constant hunger, and this results in more bites on humans.

If the bacteria happen to enter the bloodstream rather than the lymph or lungs, they multiply in the blood, causing bacteremia and severe sepsis.

In septicemic plague, bacterial endotoxins cause disseminated intravascular coagulation (DIC), where tiny blood clots form throughout the body, commonly resulting in localised ischemic necrosis, tissue death from lack of circulation and perfusion.

[citation needed] DIC results in depletion of the body's clotting resources, so that it can no longer control bleeding.

Outdoor activities such as hiking, camping, or hunting where plague-infected animals may be found, increase the risk of contracting septicemic plague, and so do certain occupations such as veterinary or other animal-related work.

[citation needed] Major port cities and trade centres such as Venice and Florence were hit the hardest.

The massive loss of the working population in Europe following the Black Death, resulting in the increased economic bargaining power of the serf labour force, was a major precipitating factor for the Peasants' Revolt of 1381.

[citation needed] Septicemic plague is a zoonosis,[11] a disease that generally is acquired by humans from animals, such as rodents and carnivores.

[12] Areas west of the Great Plains of North America are one region where plague-infected animals commonly occur.

[citation needed] Animals that commonly carry plague bacteria are large rodents and Leporidae, but carnivores sometimes also become infected by their prey.