Pneumonic plague is the only contagious infection associated with the bacteria Yersinia pestis. It is far less common than bubonic plague, but more deadly. It occurs when the bacteria reaches the lungs and is aerosolized through coughing. It can develop when the bubonic or septicemic plague reaches the lungs. Very rarely, it can be contracted if exposed to aerosolized blood from an infected animal. When it reaches the lungs of another patient, it leads to quickly developing pneumonia, usually followed by bleeding in the respiratory tract. If untreated after initial lung symptoms occur, it is usually fatal.
Antibiotics are usually effective if administered within 24 hours of the appearance of symptoms. In addition, anyone in contact with the patient should also be given a 7 day course of antibiotics. Medical personnel should take additional precautions, such as tight fitting surgical masks, to prevent infection.