The most recent widespread attack of the bubonic plague peaked in 1907 in India, where it killed 1.2 million persons. During this outbreak, designated the Third Pandemic, researchers learned much about the biology of plague—its cause, reservoirs, vectors, and mechanisms of attack—as well as some human defensive strategies against the disease. Despite these advances in understanding, the plague continued to expand its geographic range and remained a dangerous disease.
In 1907, more than 1.2 million people died of plague in India. Plague deaths were lower in preceding years and declined again in subsequent years, although they were substantial in both time periods; more than 12 million Indians died of plague during the entire period known as the Third Pandemic. Peak years for plague deaths fell around 1900 in many countries involved in the Third Pandemic, and, as the term “pandemic” connotes, most countries in the world were involved. A pandemic is the spread of a disease throughout the known world.
The first plague pandemic occurred in the sixth century; this pandemic is known as the Justinian Plague because Justinian was the Roman emperor at the time. The second plague pandemic included the catastrophic Black Death of the fourteenth century and continued, by some definitions, through the London Plague of 1665. Between the pandemics, plague occurred much less frequently, with occasional epidemics springing up. (An epidemic is a local outbreak of a disease, not nearly as widespread as a pandemic, but locally often as deadly.)
The Third Pandemic started in the 1850’s in China; it subsequently spread to Hong Kong and India and then throughout the world. It peaked in the late nineteenth and early twentieth centuries, and ended in the 1950’s. Both the pandemic’s starting and ending dates are necessarily imprecise, and some authorities argue that the Third Pandemic continued into the twenty-first century. During the Third Pandemic, researchers made great advances in understanding and dealing with the plague. In addition to its tragic effects, the Third Pandemic should be remembered for this dramatic increase in understanding. However, in addition to the mortality it caused in its old haunts, during the Third Pandemic the plague spread to continents that had not previously experienced its decimation.
During the Third Pandemic, scientists Alexandre Yersin and Shibasaburo Kitasato, working independently, discovered the bacterium that causes the plague, now known as Yersinia pestis. Yersin called it Bacterium pestis, and it was renamed twice (Bacillus pestis and Pasteurella pestis) before it was changed again in 1970 to honor Yersin’s role in its discovery. Identification of this causative organism gave scientists a target for the development of defensive strategies against the plague as well as something precise to identify in diagnosing the disease.
Rats (Rattus rattus) associated with human populations had long been linked with the plague. Large numbers of rats died in most plague epidemics, but they were thought to be fellow victims of the outbreak, not part of the problem. During the Third Pandemic, Yersin and others suggested that rats might play a more direct role in plague epidemics and pandemics, acting as the source of the bacterium during these times.
Researcher Paul-Louis Simond, working in Bombay (Mumbai), India, demonstrated that rat fleas (Xenopsylla cheopis) transferred the plague bacterium from rat to rat and from rats, especially dead rats, to humans. His work was rejected, however, because entrenched wisdom held that plague was spread through contaminated food or entered the body through cuts in the skin, and that rat fleas did not bite humans. Eventually, studies in Australia and Bombay confirmed his conclusions in all important details. This discovery gave health workers two targets to exploit in blocking the spread of plague: rat and flea populations.
Bacteriologist Waldemar Mordecai Wolff Haffkine, also working in Bombay during the Third Pandemic, developed immunological tools for treatment of and protection from the plague. He developed a plague antiserum, a passive immunity technique, in which antibodies that fight the plague bacterium were produced in other animals and then injected into humans as a defense against a plague infection in progress. The antiserum had a number of undesirable side effects and was ineffective, so Haffkine turned to active immunization, in which killed Yersinia pestis cells were injected into humans as protection against an anticipated future attack by the bacterium. In response to the dead plague cells, vaccinated humans make their own antibodies against the bacterium. This approach proved to be more effective than the passive antiserum, although it had serious side effects and was not as effective as immunization has been against other diseases, smallpox for example.
Late in the Third Pandemic, researchers found that sulfa drugs
During the Third Pandemic it was also discovered that many mammals other than rats were attacked by the plague bacterium. Many rodents—marmots, ground squirrels, prairie dogs, rats, mice, and voles—were found to be susceptible to plague parasitism, as were many other mammals (including cats and dogs). Most species were decimated by the parasite, as rats and humans were, but a few were relatively resistant to the plague bacterium. The reservoir for plague, the place it “hid” between pandemics, was found in the relatively resistant ground squirrels and marmots of the central Asian plains. Similar reservoirs were established on all continents except Australia and Antarctica during the Third Pandemic.
Fleas other than the rat flea were also found to harbor and transmit the plague bacterium, although transmission by these other fleas was not generally as efficient as that by the rat flea. The versatility of the plague bacterium in the number of mammalian hosts and flea vectors it used, and in other regards, made it apparent that plague would not be an easy opponent to vanquish.
Before the Third Pandemic, plague had been restricted to Eurasia and northern Africa. During the Third Pandemic, however, it was dispersed to North and South America, southern Africa, Madagascar, and Australia—essentially worldwide—and it became established in all those places except Australia. The Third Pandemic stands as the most widespread of the plague pandemics.
Scientists came to understand the plague during the Third Pandemic, which was epidemiologically centered in India and China, and temporally centered on the 1907 peak of deaths in India. The causative organism, the reservoirs in which plague lurked between pandemics, and the disease’s alternate hosts, vectors, and mechanisms of transmission were all discovered during the Third Pandemic. This knowledge suggested several targets for control of plague outbreaks. Control of rat and flea populations proved helpful, but so many species of rodents and fleas were involved that it was difficult to eliminate plague using this tactic alone.
Immunological attempts, although helpful, were not as effective as they have been in combating some other diseases. Sulfa drugs and certain antibiotics proved to be very effective when administered early in the progression of the disease, but plague is often misdiagnosed, and it progresses so rapidly that even these powerful tools proved to be less useful than initially hoped. In addition, Yersinia pestis, like many other troublesome bacteria, readily develops resistance to drugs.
Perhaps the most important (and discouraging) thing learned from the Third Pandemic concerns the versatility of Yersinia pestis, which makes it very unlikely that plague can be eliminated as smallpox has been. It is such a dangerous disease organism that several countries have attempted to develop plague into a biological weapon. Yersinia pestis engineered to be resistant to antiplague drugs would be a fearsome weapon. Despite the pessimism caused by the plague bacterium’s versatility and its potential as a weapon, the knowledge derived from the Third Pandemic may allow scientists to prevent a fourth plague pandemic.
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Catanach, I. J. “The ’Globalization’ of Disease? India and the Plague.” Journal of World History 12, no. 1 (2001): 131-153. Explores the dispersal of diseases using the spread of plague in the Third Pandemic, especially in India, as a central example. -
Chandavarkar, Rajnarayan. “Plague Panic and Epidemic Politics in India, 1896-1914.” In Epidemics and Ideas: Essays on the Historical Perception of Pestilence, edited by Terence Ranger and Paul Slack. Cambridge, England: Cambridge University Press, 1992. Considers the cultural and political conflicts during the most intense years of the Third Pandemic in India. -
Echenberg, Myron. “Pestis Redux: The Initial Years of the Third Bubonic Plague Pandemic, 1894-1901.” Journal of World History 13, no. 2 (2002): 429-449. Explores the early stages of the Third Pandemic, which led to 1907’s peak in the death count. -
Gregg, Charles T. Plague: An Ancient Disease in the Twentieth Century. Rev. ed. Albuquerque: University of New Mexico Press, 1985. Considers all three plague pandemics and emphasizes the continued danger of plague as a natural disease and as a biological weapon. -
Orent, Wendy. Plague: The Mysterious Past and Terrifying Future of the World’s Most Dangerous Disease. New York: Free Press, 2004. Describes the three pandemics and emphasizes the plague’s potential as a biological weapon.
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