The Seven Deadliest Plagues in History

The Black Death, 1331 to 1353

The Black Death decimated the population across Europe, Asia and Africa in the 14^th century. Not only did the Black Death cause massive numbers of deaths, it also facilitated significant social change across Europe and elsewhere.

Like the Plague of Justinian, the Black Death was caused by Yersinia pestis. Yersinia pestis is carried and spread by rodent fleas, making transmission nearly inevitable. The Black Death likely originated in India or China, spreading along the Silk Road. As early as 1331, plagues began in China, perhaps killing as many as 25 million in China. In 1338 and 1339, graves in Kyrgyzstan record a plague, perhaps Yersinia pestis. Yersinia pestis can cause three different variants of plague; bubonic, pneumonic, and septicemic. Bubonic plague is the least fatal, but still resulted in death in 30 to 75 percent of those that contracted it.

By the end of 1346, Europeans were aware that plague had already destroyed the populations of cities in India, Mesopotamia, Syria and Armenia. Plague likely entered Europe through the Genoese ships fleeing plague elsewhere. These 12 ships quickly spread plague throughout port cities in Europe, including Venice, Marseilles, and Pisa.

By 1348, the Black Death had spread through France, Spain, Portugal, Italy and England. It moved east into Germany and Scandinavia between 1348 and 1350, and entered Russia in 1351. Between 1347 and 1351, the Black Death also spread throughout the Middle East, also along common trade routes. Isolated regions were less likely to experience plague than more cosmopolitan areas.

Death rates varied depending on region, but in Europe, around 45 to 50 percent of the overall population died, with higher numbers in the south and lower ones in the east. In the Middle East, around 30 percent of the population perished. Research suggests that the death toll in Eurasia was between 75 and 200 million people.

The dramatically reduced population led to significant increases in quality of life for the lower classes. Many of the survivors had inherited wealth and land due to the deaths, but also, could now demand much higher wages for their labor.

The Third Pandemic, 1855 to 1959

The Third Pandemic shares some strong similarities with both the Plague of Justinian and the Black Death. Like both of these, it was an outbreak of Yersinia pestis originating in China. While the plague originated in the Yunnan Province of China, it spread through the rest of China due to political unrest. In Canton, 60,000 people died in only a few weeks. The numbers were higher in Hong Kong. The plague spread rapidly along shipping routes, reaching ports as far away as Australia and San Francisco.

Two different strains of Yersinia pestis were common during the Third Pandemic. The first was bubonic, the second pneumonic. The pneumonic variant was prevalent in Manchuria and Mongolia. Pneumonic plague likely had strong person-to-person transmission.

Most notably, the Third Pandemic did not die out quickly. In fact, recurrences of the Third Pandemic continued well into the 20^th century. Colonial India was particularly impacted by the Third Pandemic, with 12.5 million people dying over a thirty-year period. In India, the British developed a vaccine against bubonic plague in 1897 and began a mass vaccination campaign to reduce the prevalence of the illness. Vaccination was not compulsory, but the management programs created to reduce the plague were key in developing India’s public health system.

The last significant outbreak of the Third Pandemic occurred in Peru and Argentina in 1945. The Third Pandemic is considered to have ended in 1959; however, there are approximately 5,000 cases of plague each year. Pneumonic plague continues to have relatively high fatality rates, if treatment is not initiated quite rapidly. Bubonic plague is typically successfully treated with antibiotics.

Spanish Flu of 1918 to 1919

The Spanish Flu of 1918 or the influenza pandemic killed between 20 and 40 million people in 1918 and 1919. The Spanish Flu was more devastating than World War I, in terms of the numbers lost. The Spanish Flu was exceptionally virulent, and unusually lethal. Like other plagues, this one spread with shipping, trade, and the movement of armies.

Fatality rates were around 2.5 percent; in comparison to Yersinia pestis, that seems quite low; however, the illness spread very easily, so infection rates were astonishing. In addition, the majority of deaths came in individuals between 20 and 40 years of age. This is in direct opposition to the normal deaths associated with influenza, which typically kills the very young and very old.

There is relatively little understanding of the specifics of the Spanish Flu, but it is believed to have originated with a genetic mutation in China. This was not the first flu pandemic; a virulent strain of influenza had impacted much of the world in 1890. Those that had survived the flu in 1890 had some resistance in 1918.

Treatments available were minimal; scientists were aware of and understood microorganisms, but believed that influenza was bacterial, not viral. Initial symptoms included a high fever, sore throat, body aches, and headache. Vomiting and diarrhea was sometimes present. Many people recovered, then relapsed, with much more serious respiratory symptoms, including pulmonary hemorrhage.

Efforts were made to produce a vaccine, but these were ineffective at the time. The disease moved quickly, causing economic disruption, but left as quickly as it came, typically exhausting itself within a single community within just a few weeks. The pandemic was largely forgotten, and more than a decade would pass before the isolation of the influenza virus.

HIV/AIDS 1981 to present

The most significant pandemic of our time is HIV/AIDS. AIDS was first identified in 1981, and spread through gay men in the United States. It was, at the time, always lethal. In total, over the course of the epidemic, around 70 million people have been infected with HIV, and around 35 million people have died.

By 1983, scientists had identified the link between HIV and AIDS, recognizing that HIV caused AIDS. The number of HIV infections increased quickly, peaking in 1997. AIDS-related deaths peaked in the mid-2000s. HIV is spread through sexual contact, intravenous drug use, and from mother to child.

Today, access to antiretroviral therapies can reduce the risk of AIDS-related deaths. Many people can live healthy lives for many years with antiretroviral therapies, and approximately 39 percent of those infected with HIV take such medications. In addition, the reduced viral load associated with these medications lowers the risk of transmission. Unfortunately, three out of five people infected with HIV do not have access to life-saving antiretroviral medications. Without treatment, HIV eventually damages and destroys the body’s immune system.

The global pandemic has been largely controlled in many parts of the developed world, with reductions in new infections and in deaths from AIDS-related causes. Today, the most significant toll of HIV/AIDS is in Sub-Saharan Africa. Two-thirds of new HIV infections in 2014 occurred in Sub-Saharan Africa. In addition, these are the populations least likely to have access to antiretroviral drug therapies. In Sub-Saharan Africa, more than one out of every 25 people, or 4.7 percent of the population, is infected with HIV.