Plague

Plague, term applied indiscriminately in the Middle Ages to all fatal epidemic diseases, but now restricted to an acute, infectious, contagious disease of rodents and humans, caused by a short, thick, gram-negative bacillus, Yersinia pestis. In humans, plague occurs in three forms: bubonic plague, pneumonic plague, and septicaemic plague. Bubonic plague is the best-known form and is so called because it is characterized by the appearance of buboes, or enlarged, inflamed lymph nodes, in the groin, armpit, or on the neck. Bubonic plague is transmitted by the bite of any of numerous insects that are normally parasitic on rodents, and that seek new hosts when the original host dies. The most important of these insects is the rat flea Xenopsylla cheopis, which is parasitic on the brown rat. Pneumonic plague, so called because the lung is the site of infection, is most often transmitted by droplets sprayed from the lungs and mouth of infected people; the infection may spread from the lungs to other parts of the body, resulting in septicaemic plague, which is infection of the blood. Septicaemic plague may also be initiated by direct contact of contaminated hands, food, or objects with the mucous membranes of the nose or throat.

Untreated bubonic plague is fatal in 30 to 75 per cent of all cases, pneumonic plague 95 per cent of the time, and septicaemic plague almost invariably. Mortality in treated cases is 5 to 10 per cent.

In bubonic plague, the first symptoms are headache, nausea, vomiting, aching joints, and a general feeling of ill health. The lymph nodes of the groin or, less commonly, of the armpit or neck, suddenly become painful and swollen. The temperature, accompanied by shivering, rises to between 38.3° and 40.5° C (101° and 105° F). The pulse rate and respiration rate are increased, and the victim becomes exhausted and apathetic. The buboes swell until they approximate a chicken egg in size. In nonfatal cases, the temperature begins to fall in about five days, and approaches normal in about two weeks. In fatal cases, death results in about four days. In primary pneumonic plague, the sputum is at first slimy and tinted with blood; it later becomes free-flowing and bright red. Death occurs in most cases two or three days after the first appearance of symptoms. In primary septicaemic plague, the victim has a sudden onset of high fever and turns deep purple in several hours, often dying within the same day that symptoms first develop. The purple colour, which appears in all plague victims during their last hours, is due to respiratory failure; the popular name Black Death that is applied to the disease is derived from this symptom.

Many preventive measures, such as sanitation, killing of rats, and prevention of the transport of rats in ships arriving from ports in which the disease is endemic, are effective in reducing the incidence of plague. Famine, which reduces resistance to the disease, results in spread of plague. Individuals who have contracted the disease are isolated, put to bed, and fed fluids and easily digestible foods. Sedatives are used to reduce pain and to quiet delirium. During World War II, scientists using sulpha drugs were able to produce cures of plague; subsequently, streptomycin and tetracyclines were found to be more effective in controlling the disease.

Plague has been known for at least 3,000 years. Epidemics have been recorded in China since 224 bc. The disease occurred in huge pandemics that destroyed the entire populations of cities throughout the Middle Ages; they have occurred sporadically since that time. The last great pandemic began in China in 1894 and spread to Africa, the Pacific islands, Australia, and the Americas, reaching San Francisco in 1900. Plague still occurs in Asia, Africa, South America, and Australia, but rarely appears in Europe or the United States. In 1950 the World Health Organization initiated sanitation programmes for plague control throughout the world.