The classification of plague depends on the mode of infection and the clinical syndrome. Plague can be classified into bubonic plague, septicemic plague, or pneumonic plague.

Bubonic plague is transmitted by flea bite or direct contamination of an open skin lesion by plague-infected material. The infection spreads to the regional lymph nodes causing inflammation and swelling in one or several nodes (buboes).^[1]

Pneumonic plague occurs in two distinct and epidemiologically significant forms.^[1]

• Secondary plague pneumonia results from the hematogenous spread of Y. pestis to the lungs.
• A primary pneumonic plague patient usually presents with an infectious pneumonitis upon the onset of symptoms.

Septicemic plague can be primary or secondary to bubonic plague. Primary septicemic plague is a progressive, overwhelming bloodstream infection with Y. pestis in the apparent absence of a primary lymphadenopathy.^[1]

• Cellulocutaneous plague
• Meningeal plague
• Pharyngeal plague
• Abortive plague
• Pestis minor
• Asymptomatic plague