The plague is a serious bacterial infection that can be deadly. Sometimes referred to as the “black plague,” the disease is caused by a bacterial strain called Yersinia pestis. This bacterium is found in animals throughout the world and is usually transmitted to humans through fleas.

The plague bacteria can be transmitted to humans in the following ways: Flea bite:Flea bite exposure may result in primary bubonic plague or septicemic plague. Contact with contaminated fluid or tissue:Humans can become infected when handling tissue or body fluids of a plague-infected animal. This form of exposure most commonly results in bubonic plague or septicemic plague.

Plague is caused by the bacteria Yersinia pestis, a zoonotic bacteria usually found in small mammals and their fleas. People infected with Y. pestis often develop symptoms after an incubation period of one to seven days. There are two main clinical forms of plague infection: bubonic and pneumonic.

The name comes from the black buboes (infected lymph glands) which broke out over a plague victim's body. The cause of the plague was the bacterium Yersinia pestis, which was carried by fleas on rodents, usually rats, but this was not known to the people of the medieval period, as it was only identified in 1894 CE.