Plague is an infectious disease. The causative organism is a bacteria Yersinia pestis.
Generally rats are the carrying agents fleas. These fleas inurn actually carry the bacteria with them. Once bitten by the infected flea, the infection gets transmitted. But the rats and the fleas are only the major transmitting agents. The bacterium survives in many more species and quickly spreads. It is known to cause major pandemics.
The plague has been considered as a cause of the few really major historic pandemics or the epidemics spread over a large and multiple regions, worldwide.
The lung infection, secondary to plague called pneumonic plague is known to spread via tiny droplets spread through cough or sneeze. Their inhalation is infectious. The plague has been considered as a cause of the few really major historic pandemics or the epidemics spread over a large and multiple regions, worldwide.
United States witnesses approximately 18 cases every year. Outside the United States, the there are average reported 1,666 cases from 1967-1993.
These are the few countries which have shown highest infected cases of plague. Viz. Tanzania, Zaire, Peru, Vietnam, Madagascar, Burma, Brazil, Uganda, China Burma etc.