Septicemic plague
Septicemic plague can cause the blood to form small blood clots through the body. Without treatment it is almost always fatal. The death rate in medieval times was 99-100 percent. Septicemic plague is the rarest of the three plagues that struck Europe in 1348, the other forms are bubonic and pneumonic plague. This disease is caused mainly by the bite of an infected rodent or insect. In rare cases it can also enter the body through an opening in the skin or by cough from another infected human.