What is the deadliest form/type of plague?

Pneumonic plague is considered the deadliest form of plague due to its ability to spread directly between humans through respiratory droplets. This form of plague affects the lungs, leading to severe respiratory illness, and can progress rapidly, often resulting in death within 24 to 72 hours if left untreated. The speed of onset and the mode of transmission make pneumonic plague exceptionally dangerous in outbreak scenarios.

While both bubonic and septicemic plague are serious, they are typically not as contagious. Bubonic plague, characterized by swollen lymph nodes, is primarily transmitted through flea bites or contact with infected animals. Septicemic plague can occur as a complication of bubonic plague or through direct infection, leading to systemic illness but is less communicable in comparison to pneumonic plague.

The rapid transmission, combined with the severe impact on respiratory function, underscores why pneumonic plague is viewed as the most lethal form of this infectious disease.