What is the rarest plague?
Pneumonic plague is the rarest, but most severe form of the disease. It is 100 percent fatal if not treated rapidly and is deadly in up to half of all cases, even with prompt antibiotic treatment. Untreated cases of bubonic or septicemic plague can become pneumonic plague as infection spreads to the lungs. The death rate for persons with untreated primary pneumonic plague was reported to be almost 100% (1); the death rate for persons treated for primary pneumonic plague was 50% (1).