- The most common form of the Black Death was the bubonic plague. It was caused by the bacterium *Yersinia pestis*, which was carried by fleas that lived on rats.
- Symptoms included fever, chills, and the formation of buboes, or swollen lymph nodes, in the neck, armpits, and groin.
- The bubonic plague was often fatal, with a mortality rate of up to 50%.
Pneumonic Plague
- The pneumonic form of the Black Death was less common but more deadly than the bubonic plague. It was caused by the same bacterium (*Yersinia pestis*), but it spread through the air rather than through fleas.
- Symptoms included fever, chills, cough, and shortness of breath.
- The pneumonic plague was often fatal, with a mortality rate of up to 90%.
Septicemic Plague
- The septicemic form of the Black Death was the least common but most deadly form of the disease. It was caused by the same bacterium (*Yersinia pestis*), but it spread through the bloodstream rather than through fleas or the air.
- Symptoms included fever, chills, and a rapid decline in health.
- The septicemic plague was often fatal within 24 hours.