India, Oct. 5 -- Nearly 200 people have been placed under medical observation after a laboratory worker died from suspected pneumonic plague in Siberia's Irkutsk region, according to a report by The Moscow Times.

According to the World Health Organization (WHO), plague is caused by the bacteria Yersinia pestis, 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, it notes.

Bubonic plague is the most common clinical form of plague. Bubonic plague is characterised by painful swollen lymph nodes or 'buboes'. Less common, but severe forms include septicaemic and pneumonic plague.

According to the WHO, plague is transmitted b...