Pneumonic plague is a severe lung infection caused by the bacterium Yersinia pestis. It is a form of the plague that can spread from person to person through respiratory droplets, making it highly contagious. Symptoms include fever, chills, cough, and difficulty breathing, often developing rapidly. If left untreated, pneumonic plague can lead to serious complications and death within days. Early diagnosis and treatment with antibiotics are crucial for recovery. The disease is part of the broader category of plague, which also includes bubonic plague and septicemic plague, both of which have different modes of transmission and symptoms.