Plague types: pneumonic, bubonic, and septicemic symptoms explained

The plague, caused by the Yersinia pestis bacterium, has three forms—pneumonic, bubonic, and septicemic—each with distinct symptoms and transmission methods, as detailed by Italy's Istituto Superiore di Sanità. The pneumonic form, which infects the lungs, is the most dangerous due to person-to-person airborne transmission. The bubonic plague, the most common, spreads via infected flea bites and causes swollen lymph nodes, but does not transmit between people. The septicemic form occurs when the bacterium multiplies in the blood, causing severe symptoms like bleeding and shock, also without human-to-human transmission. Historically, the plague killed nearly a third of Europe's population in the 1350s and caused a pandemic in late 19th-century China that killed 12 million people. Recent concerns stem from the suspected plague death of a Russian researcher, though experts say risks remain limited.