Bubonic Plague: Yesterday's Scourge--and Tomorrow's?

by Tina Blue
December 20, 2000

          When you think of bubonic plague, no doubt you think of the Black Death, the scourge of medieval Europe. What you probably don't realize is that since the start of the twentieth century, North America has been the world's largest reservoir of infection for bubonic plague and that every year in this country people are infected with the plague and some die of it.

     What you also may not realize is that the antibiotics used to treat plague are not as effective as they once were, and that eventually, perhaps in the not too distant future, they will lose their efficacy altogether. When that happens, we will see a worldwide pandemic that will vastly overshadow the Black Death pandemic that depopulated Europe during the Middle Ages.

          The organism responsible for bubonic plague is Pasteurella pestis (also called Yersinia pestis), which is spread by rodents and transmitted to man by fleas parasitic on rodents.

          The disease gets its name from one of its most characteristic signs, a painful swelling of the lymph nodes in the groin area. The Greek word for groin (boubon) is the root of the word "bubo," which is used to refer to that swelling. A plague bubo can get as big as a large orange.

          Lymph nodes in other parts of the body can also swell from the infection, but the groin area is most often involved because it is easy for an infected flea to reach and bite the legs, so the lymph nodes in the groin provide the most convenient site for P.
to set up shop.

          The early signs of plague are easily mistaken for flu or other illnesses: fever, chills, and weakness to the point of severe prostration. Plague's ability to masquerade as flu in the early stages is particularly unfortunate, since successful treatment depends on using the appropriate antibiotics within a narrow time frame. Streptomycin, aureomycin, and chloramphenicol are usually effective if administered in the early stages of the disease. (Sometimes tetracycline is used in addition to bolster the effect of one of those three antibiotics.)

          Even in cases of pneumonic plague, which is far more virulent and progresses even more rapidly than bubonic plague, if proper treatment is begun within twenty-four hours of onset, a cure is possible. Where pneumonic plague, the most virulent form of the disease, is concerned, if treatment is begun after that twenty-four hour window has closed, the antibiotics will do no good.

          An early diagnosis of plague is essential for another reason. Penicillin is useless against P. pestis, and if the physician mistakes plague symptoms for those of another disease, precious time may be lost while the wrong antibiotics are administered and given time to take effect. (Although penicillin is not effective against P. pestis, it is sometimes used in plague cases to treat secondary infections.)

          Before the more effective drugs were developed, sulfadiazine was used with some success to treat plague, and even now it is used if the appropriate antibiotics are not available or if they are in short supply. Sulfadiazine is frequently combined with the antibiotics, to enhance their effectiveness, but most often it is used as a form of chemoprophylactic (preventive) protection for those who have come in contact with plague victims but who as yet show no sign of infection.

          The Pasteurella pestis organism causes hemorrhages, which are called plague spots when they appear on the skin. The dark color of the spots and the extremely high mortality rate of the disease combined to give bubonic plague its popular name during the Middle Ages, the Black Death.

          Bubonic plague is not directly communicable from one human to another; it must be transmitted by the bite of an infected flea. But the pneumonic form of the disease, which develops as a particularly virulent form of pneumonia, can be directly transmitted. In pneumonic plague, the bacilli are discharged into the atmosphere during coughing or sneezing, or even during labored breathing. This form of the disease is highly contagious, and the mortality rate for untreated pneumonic plague is virtually 100%. Even when treatment is administered quickly, recovery is by no means guaranteed.


          Plague persists as a chronic disease among approximately two hundred species of rodents around the world. In this form, referred to as "sylvatic plague," it is widely distributed in western North America, southern South America, southern Africa, the Middle East, and central Asia. These sylvatic plague reservoirs provide the infected fleas that under optimal conditions (optimal for the disease organism, not for its victims) will infect rats and man. The infection is passed from wild rodents to "domestic" rodents--those inhabiting large cities in close association with man.

          Until the first years of the twentieth century, plague was unknown in North and South America. That is ironic, since those two continents now constitute the world's largest loci of infection. The infection of the "New World" occurred as a consequence of the third great plague pandemic, which officially began in 1894, though many experts cite 1850 as its real starting point.

          The first pandemic occurred during the sixth century a.d., during the reign of the Emperor Justinian. The second pandemic occurred during the Middle Ages--it is the one we call the Black Death. The third pandemic lasted until 1959. Many of you who are reading this article don't realize it, but you are a survivor of the third great bubonic plague pandemic, which killed far more people--over thirteen million!--than the other two pandemics combined.

          In 1894 a few cases of plague were documented in Canton, and from there it spread to Hong Kong. Although the initial outbreak was relatively small, the disease was quickly carried to many parts of the world by ocean-going vessels. In its westward course, the plague reached India, and then Africa and Europe (especially Spain, Portugal, Italy, and Great Britain). It also spread eastward to the Philippines, Australia, Japan, Hawaii, and the Pacific coasts of North and South America.


          Human plague was diagnosed for the first time in the United States in 1900, at San Francisco, and shown to be present among rats in that city in 1902. At first business interests, in collusion with conservative politicians in both the city and the state, resisted official acknowledgment of plague as well as all official efforts to control its spread. This refusal to address the problem for fear of hurting business led to a far worse outbreak than would otherwise have occurred. Eventually, other states quarantined California, and forced them to deal with the plague after all.

          Many of the deaths during the third pandemic were concentrated in the less developed parts of the world, especially in India between 1898 and 1928. There were several hundred plague deaths in the United States during the last century, including several in the 1990s.

          At present the plague is largely controlled throughout the world, but it remains endemic in some rural areas of Asia, South Africa, and South America. Sometimes, as in Vietnam during the 1960s, as a result of war conditions, it flares up into epidemic proportions.


     One reason why we need to maintain a healthy respect for the possibility of another great plague pandemic is that although the reservoirs of infection are rural, human commerce, urban living conditions, population density, and encroachment on and development of wilderness areas significantly influence the conditions that lead to the spread of plague.

          The introduction of DDT during World War II was a major step in getting control  of P. pestis. The U.S. military used DDT to suppress fleas in 1944 at Dakar, Senegal. There was also a directed effort to educate the inhabitants of the region in sanitation methods and rat control.

          Other preventive measures against plague include ratproofing buildings and reducing living and breeding sites for rats, especially docks and warehouses. Ships are also ratproofed and periodically fumigated, and vessels and cargoes from plague areas are inspected for rats. Periodic surveys are taken in endemic and potentially epidemic areas to assess the prevalence of rats and fleas, and rat populations in urban areas are suppressed by means of poisoning and trapping.

          When a plague outbreak occurs, the governments of the nations involved are required by international law to notify the World Health Organization (WHO) as well as the governments of adjacent countries.

          Despite such precautions, however, the ease and speed of global travel have created a situation where any communicable disease is likely to escape its place of origin. Furthermore, many agencies--both national and international--responsible for monitoring and controlling potential plague outbreaks are chronically underfunded and understaffed, since most of the world's governments have grown complacent about the risk of a fourth plague pandemic.

          Their complacency is far from warranted. In the first place, rodenticides and insecticides used to control rat and flea populations in urban areas are no longer as effective as they once were. In several U.S. cities, between one-fourth and one-half of all rats and mice are now resistant to warfarin and to other chemical agents used to control them. DDT is no longer as effective in flea control, and, besides, it is widely banned in the advanced nations.

          In the second place, it may not be long before antibiotics used to treat plague become completely useless against the disease. In 1998, the first case of human plague that showed total resistance to all known antibiotics was reported. Even one such strain of resistant P. pestis could spell catastrophe. Once a bacterium develops resistance to a drug, that resistance soon spreads to all such bacteria by a process called "infectious drug resistance." Some bacteria carry an "R" (for "resistance") factor, and can pass their resistance along, not only to the same bacteria, but even to other bacteria altogether.

          Escherichia coli, the common colon bacillus, is frequently resistant to one or more antimicrobial drugs. Some strains of E. coli are resistant to all known antimicrobials. And E. coli often carry R factors. So a common bacterium found in the human body and in river water all over the world can pass antimicrobial resistance to a wide variety of disease-causing organisms--including P. pestis.

          If an outbreak of multiply resistant plague occurs anywhere in the world, the chances are high that it will spread globally. Should that occur, our innumerable large urban centers are at great risk for epidemic plague, not only because crowded urban conditions are ideal for establishing a plague epidemic, but also because so many rodents and fleas have developed resistance to the rodenticides and insecticides we would normally use to control their populations.

          The fourth great bubonic plague pandemic could occur at almost any time. If and when it does, its effects will be far more devastating than those of the Black Death.

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