plague

A depiction of the flight of townspeople into the country to escape from the plague, in 1630. The European epidemics in the years from 1600 to 1750 were among the most devastating in human history. The new waves of the plague which struck northern Italy and Tuscany in 1630 were believed to have killed up to 70% of the population.

Term applied to any epidemic disease with a high mortality rate, but it usually refers to bubonic plague. This is a disease transmitted by fleas (carried by the black rat), which infect the sufferer with the bacillus Yersinia pestis. An early symptom is swelling of lymph nodes, usually in the armpit and groin; such swellings are called ‘buboes’. It causes virulent blood poisoning and the death rate is high.

Rarer but more virulent forms of plague are septicaemic and pneumonic; both still exert a formidable mortality. Outbreaks of plague still occur, mostly in poor countries, but never to the extent seen in the late Middle Ages. According to a World Health Organization report published in 1996, the incidence of plague is on the increase. It was reported in 13 states of the USA between 1984 and 1994, in comparison with just 3 states in the 1940s.

Transmission Y. pestis persists worldwide in certain wild rodent populations and transmission is mainly by fleas. The flea ingests the bacteria after biting an infected individual. The bacteria then multiply, forming a blockage between the flea's oesophagus and midgut. Prevented from feeding, the hungry flea bites repeatedly and with each bite it regurgitates infected blood into the bite, transmitting the bacteria.

Vaccine A new plague vaccine was under development in 1995 using a genetically engineered version of the disabled salmonella bacterium Salmonella typhi. A section of the genetic code from Y. pestis is inserted into the salmonella bacteria. When the bacteria are swallowed they live in the gut and produce a protein normally found in Y. pestis. In mice this immunizes against plague.

History The first description of the plague dates from 40 BC in Libya. The Roman Empire was swept by plague in AD 251-260. After the Black Death in the 14th century, plague remained endemic for the next three centuries, the most notorious outbreak being the Great Plague of London in 1665, when about 100,000 of the 400,000 inhabitants died. Plague claimed 300,000 victims in Prussia in 1709. In the 1980s and 1990s there were cases of plague in Africa, Latin America, and India.