PLAGUE

an infectious fever caused by the bacillus Yersinia pestis, transmitted by the rat flea. It is primarily a disease of rodents, and epidemics in human beings originate in contact with the fleas of infected rodents. The disease in man has three clinical forms: bubonic, characterized by swelling of the lymph nodes (buboes); pneumonic, in which the lungs are extensively involved; and septicemic, in which the bloodstream is so invaded by Yersinia that death ensues before the bubonic or pneumonic forms have had time to appear. Plague as spread from rats to man in crowded urban areas is sometimes called murine (rat) or urban plague; plague in desert or rural areas where the human population is sparse but the wild rodent population large and infected may be called sylvatic (woodland) or campestral (field). In the 14th century, when this disease was known as the Black Death (q.v.), some plague infections were bubonic and some were pneumonic. The number of deaths was enormous, reaching in various parts of Europe two-thirds or three-fourths of the population in the first pestilence. It has been calculated that one-fourth of the population of Europe, or 25,000,000 persons, died from plague during the great epidemic. The Great Plague of London in 166465 resulted in more than 70,000 deaths in a population estimated at 460,000. An outbreak in Canton and Hong Kong in 1894 left 80,000 to 100,000 dead, and within 20 years the disease spread from the southern Chinese ports throughout the whole world, resulting in more than 10,000,000 deaths. Plague is primarily a disease of rodents, and man enters only accidentally into the usual cycle. This cyclerodentflearodentas a rule is enzootic (present in an animal community at all times but occurring in only small numbers of cases), but under certain environmental conditions it reaches epizootic proportions (affecting many animals in any region at the same time). In some areas plague-infected rats from ships spread the infection in ports, where it became epizootic. Spread of the infection among domestic rodents in the vicinity of human habitations creates conditions favourable for outbreaks of human plague, for when an epizootic outbreak reduces the rodent population, fleas from the dead animals fail to find another rodent host and thus begin to infest man. At first the cases are sporadic, but under suitable conditions large numbers of persons may be included. The illness in man varies within the widest limits, exhibiting all gradations of severity from mere indisposition to violent death. The mild infections are almost always bubonic; pneumonic and septicemic plague are invariably severe and almost always fatal unless treated. The incubation period is usually three to six days but may be as short as 36 hours or as long as 10 days. As a rule the onset is sudden and well marked. Bubonic plague constitutes about three-fourths of plague cases. Typically, bubonic plague starts with shivering, then vomiting, headache, giddiness, intolerance to light; pain in the back and limbs; sleeplessness, apathy, or delirium. The temperature rises rapidly to 104 F (40 C) or higher and frequently falls two or three degrees on the second or third day, with marked prostration. Constipation is usual; diarrhea is a grave sign. Most characteristic is the early appearance of buboes, which are usually distributed in the groin and armpits. Bubonic plague is not directly infectious from man to man; the bacillus is carried from one person to another by the flea. In pneumonic plague the physical signs are those of bronchopneumonia; edema (filling with fluid) of the lungs soon follows; and death occurs in three or four days. Septicemic plague is marked by prostration and brain damage; death may occur within 24 hours. Septicemic plague may prove fatal before there is time for pneumonia to develop. If, however, pneumonia does occur, the patient becomes highly infectious. His contacts will contract pneumonic, not bubonic, plague. Pneumonic plague is nearly always fatal. Treatment is primarily with streptomycin, tetracycline, and sulfonamides. Penicillin is without effect against plague. The suppression of epidemic plague is attempted by appropriate sanitary measures directed simultaneously against fleas and rodents and isolation of the sick and the handling with greatest caution of all infectious material. A vaccine is available and may be used in endemic areas for people likely to be exposed to rodents and their fleas.