How did the bubonic plague happen?

The bubonic plague is caused by the bacterium *Yersinia pestis*. It is transmitted to humans by the bite of an infected flea. The fleas that carry the plague bacterium are usually found on rodents, such as rats. When a rat dies of the plague, the fleas that were living on it look for a new host to feed on. If they bite a human, they can transmit the plague bacterium to that person.

The bubonic plague is characterized by the formation of buboes, which are swollen lymph nodes. The buboes are usually found in the armpits, groin, or neck. Other symptoms of the bubonic plague include fever, chills, and weakness. If the plague bacterium enters the bloodstream, it can cause septicemic plague, which is a very serious form of the disease. Septicemic plague can lead to organ failure and death.

The bubonic plague has been responsible for several pandemics throughout history. The most famous of these pandemics was the Black Death, which killed an estimated 75 to 200 million people in the 14th century. The bubonic plague is still a threat today, but it is now rare thanks to the development of antibiotics.