WAYS OF INFECTION
When harmful microbes, or germs, enter the body, they multiply and cause disease. This is called infection. Your body's defences usually do a killer job destroying harmful microbes. But sometimes germs multiply faster than the body can destroy them- and you get sick. People come in contact with germs in many ways, including:
· Infected food or water: dangerous microbes can enter through your mouth if you drink untreated water or swallow food that's uncooked or unwashed.
· Infected creatures: harmful microbes can enter your body through contact with infected creatures.
· Germs in the air: dangerous microbes can spread through the air and enter your nose and mouth when you breathe

RESERVOIRS AND VECTORS
Plague is an infectious disease of animals and humans caused by a bacterium named Yersinia pestis. Yersinia pestis mainly infects rats and other rodents. Rodents are the prime reservoir for the bacteria. Fleas function as the prime vectors carrying the bacteria from one species to another. The fleas bite the rodents infected with Yersinia pestis and then they bite people and so transmit the disease to them. In this invisible manner the plague spread from rat to human. Wild rodents in certain areas around the world are infected with plague. Plague still occurs in rural communities or in cities. People usually get plague from being bitten by a flea that is carrying the plague bacterium or by handling an infected animal. Transmission of the plague to people can also occur from eating infected animals such as squirrels.

DIFFERENT NAMES FOR PLAGUE
The most common names were Black Death, bubonic plague and pestilence.The word "pestilence" comes from "pestis," the Latin word for "plague." The origin of this name is the fetid smelling of the open buboes. Because the plague was responsible for so many deaths, the plague and death have been associated. In Spain it was called " la peste negra" and also "la peste bubónica". The Black Death name comes from the colour of the skin. The victims of the "black plague" had bleeding below the skin (haemorrhage), which made darkened ("blackened") their bodies. The most common form of the plague was named bubonic for the characteristic buboes in the groin, neck and armpit. The word "bubo" comes from the Greek "boubon" meaning groin or swollen groin.

PNEUMONIC AND SEPTICAEMIC PLAGUES
The plague was, a highly contagious, infectious disease. Once someone has the plague, they can transmit it to another person by the air.
Pneumonic plague is an infection of the lungs by Yersina pestis. The first signs of the pneumonic plague are fever, headache, weakness, and cough producing blood. The pneumonia progresses over 2 to 4 days. Person-to-person transmission of pneumonic plague occurs through the respiratory system, which can only infect those who have face-to-face contact with the person who is ill.
Yersinia pestis can enter the blood and cause septic shock and death. This is called septicaemic plague. This is the most dangerous form of plague that can kill in just a few hours after infection. The septicaemic form of the plague killed most quickly of all, and probably explains the stories of people going to bed apparently healthy and never waking up.