Septicemic plague is the least common but most deadly of the diseases caused by the bacteria Yersinia pestis, which also causes bubonic plague and pneumonic plague.  It is a particular form of sepsis and septicemia and presents in a very similar manner, but due to the toxins released by the bacteria, the patient usually develops DIC which soon exhausts the patient's clotting factors and is followed by uncontrolled bleeding.

Septicemic plague can be caused by flea bites, animal bites, or even exposure of an open wound to anything contaminated by the bacteria.  More rarely, it can be contracted by inhaling the aerosolized bacteria from the cough of an infected person.  

Even with treatment within 24 hours of symptoms, septicemic plague can be fatal.  After 24 hours, the mortality rate increases drastically.

Septicemic plague at Wikipedia

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