The bubonic plague is a serious infectious disease caused by the bacterium Yersinia pestis. It is primarily spread through bites from infected fleas that live on rodents, especially rats. Symptoms include swollen lymph nodes, fever, and chills, which can appear suddenly. If not treated quickly, the disease can become life-threatening. Historically, the bubonic plague is most famous for causing the Black Death in the 14th century, which killed millions of people in Europe. Today, while it is rare, the disease can still occur in some parts of the world, and antibiotics are effective in treating it if caught early.