A serious infection carried by rodents and transmitted to humans by flea bites
Plague is the result of infection by the bacterium Yersinia pestis, which usually affects rodents but can be transmitted to humans through flea bites. During the Middle Ages, the disease caused pandemics (widespread epidemics), one of the largest of which was the so-called Black Death of the 14th century, which killed over 25 million people in Europe. Today, small outbreaks occur in Asia, Africa, and South America, and there are a few cases each year in the US, but plague is unknown in Europe.
There are two main forms of plague: bubonic plague, which affects the lymph nodes, and pneumonic plague, which occurs if the infection spreads to the lungs. The symptoms of both forms develop rapidly and include a high fever and chills. In bubonic plague, painful swellings known as buboes develop in the lymph nodes, usually in the groin and armpits. Pneumonic plague causes a severe cough, shortness of breath, and chest pain. Once the lungs are infected, plague can be transmitted from person to person through airborne droplets from coughs and sneezes.
Plague is diagnosed from the symptoms and by a blood test. People given immediate treatment with antibiotics usually make a complete recovery. However, if treatment is delayed, the disease is frequently fatal.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.