Solution:Plague is an infectious disease caused by the bacterium Yersinia pestis, which primarily affects wild rodents. It is spread from one rodent to another by fleas.
Humans bitten by an infected flea usually develop a bubonic form of plague, which is characterized by a bubo i.e. a swelling of the lymph node draining the flea bite site.
If the bacteria reach the lungs, the patient develops pneumonic plague. If diagnosed early, bubonic plague can be successfully treated with antibiotics. But in case of pneumonic plague, patients can die within 24 hours after infection.