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Plague is a highly fatal epidemic disease caused by a bacterial pathogen, Yersinia pestis. It is a disease of antiquity having been known some 3,000 years ago. The disease is on record of having caused devastation to kingdoms in the Middle Ages. The bacteria, Y. pestis is a gram-negative bacillus whose home is the gut of an insect, the rat flea, Xenopsylla chaeopis and hence perhaps the name 'pestis'. The flea lives as an ectoparasite on rats and other rodents and through its bites the flea transfers the bacteria into the host. The flea is therefore the agent of transmission of plague from rodent to rodent and, occasionally from rodent to human who develops symptoms of plague. An infected human then spreads the disease to others and an outbreak of human plague ensues.

It has been estimated that one-fourth of the population of Europe, or about 25,000,000 persons, died of plague in the 14th century. There were no documentary basis until the 20th century for the assumption that the second plague pandemic of the 14th century originated in central Asia and spread to Europe, to India and to China. The Great Plague of London in 1664-65 was not an isolated phenomenon. Plague had recurred frequently throughout Europe in the 15th, 16th and 17th centuries.

Once it was a maxim that plague never appears east of the Indus, but during the 19th century it afflicted more than one district of India. In 1815 Gujarat, Kathiawar and Cutch suffered epidemics after three years of severe famine. Again early the next year it struck these same localities and then extended to Sind as far as Hyderabad and Southeast as far as Ahmedabad and Dholera. But it disappeared from those parts in 1820 or early in 1821 and was not heard of again until July 1836, when it broke out with violence at the town of Pali, in Rajputana. It spread from Pali to Ajmer-Merwara but died out spontaneously in the hot season of 1837. In 1849 and 1850 and again in 1852 the disease raged and spread southward. In another outbreak in 1876-77 the symptoms of the disease, called maha murree or mahamari by the Indians, were precisely those of oriental plague, and concurrent deaths of rats were noted.

Ports in South China became plague distribution centres, and between 1894 and 1922 the disease spread throughout the whole world, more widely than during any great foregoing epidemics. Among the many points infected were Bombay in 1896 and Calcutta in 1898. India suffered most. The reported number of deaths between 1896 and 1917 was 9,841,396; the maximum, reached in 1907, was 1,315,892 - a rate of 5.16 per 1,000 of the population. Fortunately in the ensuing 25 years the incidence curve turned downward toward greatly diminished prevalence. In 1923 there were fewer than 250,000 deaths; in 1942, 10,577; in 1947, 41,745; in 1948, 9,757; and in 1952, 1007. Incomplete records for 1954 listed 157 deaths in Burma and 547 in India; those for 1955 showed 720 cases, with 162 deaths.

One manifestation of plague is the characteristic swelling of the lymph nodes of the infected individual, a condition called 'bubo'. This condition is thus known as bubonic plague with acute inflammation of the lymph nodes and associated fever and pain. In relatively mild form of the disease, the infective process stops here, that is, in the lymph nodes, but in some patients pneumonia develops due to infection of the lungs. Such cases are described as pneumonic plague, which is potent in rapid spread of the disease because the victim coughs out droplets that contain the bacteria that can easily infect healthy individuals through the nasal route. Pneumonic plague can be fatal if not treated with antibiotic immediately. Occasionally, in some patients the bacteria infects the blood and moves freely in different vital organs resulting in septicaemia and the condition is known as sceptecaemic plague. Such patients have their body turn dark red as a result of respiratory failure and without treatment will inevitably die and consequently the syndrome received the name 'Black Death'.

Plague has not been on record in Bangladesh in recent years. In 1994 there were two outbreaks in India which were rapidly contained by killing rats so as to eliminate the vector flea and by rapid detection of plague cases, their isolation and treatment with antibiotics. At that time, precautionary measures also were adopted in Bangladesh which primarily involved an awareness creation programme to make the public alert about the symptoms and urging suspected cases to report to doctors for immediate attention. It is believed that no case of plague was detected in Bangladesh at that time. [Zia Uddin Ahmed]

See also flea; rat.