plague

an acute infectious disease of man and animals, classified as a quarantine disease. The causative agent is the plague bacillus, Pasteurella pestis, discovered in 1894 by the French scientist A. Yersin (1863–1943) and the Japanese scientist Kitasato Shibasaburo (1852–1931). It is a coccoid gram-negative bacillus that grows well on ordinary culture media and is sensitive to physical and chemical factors, as well as to ordinary disinfectants. It dies within one minute of exposure to a temperature of 100°C.

Plague epidemics periodically swept many countries. The first pandemic, known in the literature as Justinian’s plague, occurred in the sixth century in the Eastern Roman Empire, affecting many countries and killing about 100 million persons in 50 years. The second pandemic, known as the Black Death, began in the 14th century. The third, which broke out at the end of the 19th century, was spread by ship rats to more than 100 ports in various countries. Occurrences of plague were recorded from the 14th century on in central and northwestern Russia, including numerous occurrences in Moscow. It occurred in Transbaikalia, Transcaucasia, and the Caspian Region in the 19th century and in Odessa and other Black Sea ports at the end of the 19th and early 20th centuries, where it was brought in by plague-infected rats. Major epidemics were recorded in India in the 20th century.

Plague is characterized by natural endemism, associated with desert, steppe, and mountain landscapes, where the epizootic process is maintained by certain rodent species; however, other rodents, as well as hares, camels, and other mammals, are also dangerous to man. The epidemiological danger increases when plague is introduced into populations of commensal rodents, such as rats. The disease is transmitted to humans by animals through fleas; less common is infection as a result of direct contact, usually contracted when dressing the carcasses of infected animals. Humans infect other humans through fleas. When the bubonic form is complicated by pneumonia (secondary pneumonic plague), the disease is spread by airborne droplets, like influenza, and the highly contagious primary pneumonic plague occurs. Depending on the mechanism of infection, the causative agent penetrates the organism through the skin, the mucosa of the upper respiratory tract, and the conjunctiva. Carriers of the plague bacillus (in the nasopharynx) have been discovered.

The incubation period of plague is two to six days. The disease is characterized by sudden onset, chills, severe headache, agitation, and mental confusion. The body temperature rises to 40°C, and hyperemia of the face is observed. Frequently, the meninges become involved. In the bubonic form painful buboes appear on different parts of the body; symptoms of pneumonia appear in the pneumonic form. The course is generally severe. Bacteriological and serological methods are used for laboratory diagnosis.

Treatment includes the administration of streptomycin and other antibiotics. Preventive measures include epidemiological reconnaissance in areas where the disease is endemic (epizootological survey and observation of human and animal populations) and the use of live vaccines. To achieve early and emergency prophylaxis, the extermination of rodents and fleas in the wild and in dwellings is vital. In the event of an epidemic, infected persons are hospitalized, and individuals who have come in contact with them are isolated and given prophylactic treatment. Disinfection and quarantine measures are also instituted.