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Plague is an infectious disease of animals and humans caused by a nasty little bacterium named Yersinia pestis. People usually get plague after being bitten by a rodent flea carrying plague bacteria, or by handling an infected animal. More rarely, people can become infected by coming in contact with the respiratory secretions (saliva, phlegm, etc) of infected persons.
During the 14th Century, there was a devastating outbreak of bubonic plague, probably originating in China, and spreading along trade routes throughout the Old World. The pandemic claimed more than 50 million lives, nearly half of which were in Europe, where more than a quarter of the population died. The catastrophe is to this day commemorated in nursery rhymes such as 'Ring-a-Ring-of-Roses'.
Today, modern antibiotics are effective against plague, but if a person is not treated promptly, the disease can still cause illness or death. In fact, more than half of all untreated plague cases result in death. Outbreaks of plague still occur worldwide in rural communities or in cities where there are great numbers of rodents. These outbreaks are usually associated with rats living in the home. During the 1970s, the majority of plague cases were reported from Asia. However, by the 1980s and 1990s the majority occurred in Africa.
Several other countries report plague cases every year. For example, around ten to 15 people are infected each year in the United States and around 14% of these cases are fatal. Infections occur chiefly in the West and South-West - the last urban plague epidemic in the US occurred in Los Angeles in 1924-25. Globally, the World Health Organization reports an average of 2,500 cases of plague every year with about 180 deaths. About 75% of cases occur in Africa but Asia and the Americas also report cases annually.
The most common form of human plague can be identified by a swollen and tender lymph gland accompanied by pain. This swollen gland is called a bubo - hence the term 'bubonic plague.' A person usually becomes ill with plague within two to six days of being infected. If bubonic plague is left untreated with specific antibiotic therapy, bacteria invade the bloodstream and rapidly multiply spreading throughout the body and causing a severe and often fatal condition.
Infection of the lungs with the plague bacterium causes the pneumonic form of plague or Plague Pneumonia. The infected person may experience high fever, chills, coughing, and have difficulty breathing. The rarest form of plague is accompanied by blood poisoning: septicaemic plague usually kills within a few days.