The pathogen behind plague
The plague bacterium, Yersinia pestis, survives innocuously in rat fleas but a chance transfer to human beings can prove fatal. A disturbance in balance between the rats and the fleas leads to death of the rats or ratfall. Epidemiologists use ratfall as an indicator of the possibility of plague.
There are three types of plagues:
BUBONIC PLAGUE: It surfaces two to six days after the bite of a rat flea. The symptoms are a sudden onset of fever, chill and headache. A swelling (or bubo) develops in the lymph node around the groin or neck region within 24 hours.
PNEUMONIC PLAGUE: It is the most feared complication of bubonic plague. It is a contagious infection in which the bacteria are transmitted from the bubo to the lungs through blood. These in turn spread through cough droplets in the air.
SEPTICAEMIC PLAGUE: It is caused by the rapid multiplication of the plague bacteria in blood, causing fever and death.