Carrier of the Black Death Variations Pneumonic plague is a more virulent form, caused in cold weather when the infection moves into the lungs and results in a form of pneumonia. The victim is wracked by fever and starts coughing up blood, which contains plague bacteria and makes transmission airborne.
Pneumonic plague is a more virulent form.
Though pneumonic plague is far less frequent than bubonic, it is much more virulent. Septicaemic plague is caused when vast numbers of Y. pestis bacilli enter the bloodstream and overwhelm the system. A rash forms within hours and death occurs within a day, before the buboes even have time to form. This form of plague is always fatal, but very rare because it is flea-borne and the victim is usually dead before transmission can occur. This limits the outbreaks to particular seasons in Europe.