What are the causes of plague?

You have certainly heard about Black Death-a bubonic plague which wiped out 25million people, approriately a third of England's population back in the 1300s. Plague is a bacterial disease, which still causes one to two thousand deaths per year. It is hard to estimate how many effects else of plague on the society, but in real life, plague is a terrible threat of human since the ancient time. In condition, what are the causes of plague?what makes plague such a tragedy of human? Accoding to scientists, the condition of climate change, the bad living condition and the people's contact with some infected animals are three main reasons that makes plague become an obsession of human.
Many scientists have proved that the outbreaks of plague appearing to be related to the climate change. The Yersinia pestis bacterium was discoveried in 1894 as the agent of plague. In moist climate condition, this bacterium become more active. A bacterium can reproduce a thousand of bacteria just in a few seconds. Taking advange of the convenience of weather, the fleas bringing this bacterium is also supported to be survival and reproductive. These parasites will follow their hosts to travel places to places and infect people with disease. Many scientists have discoveried that the Black Death in the 1300s is the result of the kind of weather condition-warm and wet. It is a good evidence to convince us that the climate change has affected on the development of plague. Nowadays, the phenomenon of global warming is affecting environmental condition worldwide. Warmer and wetter weather condition make the rate of people infected disease increase because there are more bacteria in the environment. As a result, more new outbreaks of plague found are the effect of climate change.
Plague outbreaks are most commonly found in rural areas. Rural areas are usually the poor areas with bad condition of living. These areas are normally the concentration point of overcrowding population and poor condition of hygiene,that causes rat-one of the hosts of intected fleas reproducing quickly. Besides, the economy of society is not good enough to supply residents the preventive treatment with antibiotics. Morever, the low awareness of residents in the consequence of plague is also a prolem. These residents usually donot report their infected relatives or animals to health department. Consequently, the work of seperating the patients can not be done well, and it is the main cause why plague spreads so quickly. These residents are also lack of the coorperation with their authorities in mission of killing in fleas, rats and infected animals. In fact, it is hard for the authorities to control the situation of plague in rural ares.
People can also be infected plague by contacting with some certain animals. Rats, quirrels, rabbits and lice are common sources of infection. Sometimes, pets like cats and dogs may become infected by such animals and make tranmission into human's body. People may easily get infection of plague just by a fleabite. The bacteria of plague can also enter human's blood through a little cut in skin if human handle or touch these animals. One other path help bacteria go straight into human's body is through the breath. People can breathe into lung an amount of bacteria of plague coughed by infected animals. These bacteria will travel to all organs following the bloodstream and they will soon invade human's body and make the outbreak of plague as we already know. Plague can spread with a threaten speed over a large of population, as well as the rapid reproduction of these animals risk to human when we contact with them.
We now maybe live in better condition, but can not forget the tragedy of death caused by plague since the past. There remain victims of plague on over the world who maybe are suffering the pain because of plague. In fact, plague, caused by the changing climate, the bad condition of living and the contact with infected animals, will be a bigger prolem in the future if human cannot find any method to prevent or make less effects from it.