Pandemics

DEFINITION: Outbreaks of infectious diseases that affect large numbers of people over large geographic areas

Pandemics have long affected global human populations, often killing substantial numbers of people, weakening many others, and causing economic distress. Because of advances in medicine and disease research, some infectious diseases have become less likely to pose pandemic threats, but increased global travel in the twenty-first century increases the likelihood that other diseases may become pandemics.

The spread of several infectious diseases—including plague, cholera, influenza, typhus, smallpox, malaria, and yellow fever—have reached pandemic levels throughout history. Such large-scale outbreaks have continued into more modern times. The 1918–19 influenza pandemic is estimated to have killed between 20 million and 40 million people worldwide. By the early twenty-first century acquired immunodeficiency syndrome (AIDS), which is caused by the human immunodeficiency virus (HIV), had reached pandemic status, with large numbers of cases appearing in all regions of the world and close to 40 million deaths recorded. In 2009, influenza again reached pandemic proportions, although the death rate was much lower than in the earlier pandemic. Public health officials worked hard to prevent the 2014–16 Ebola epidemic in West Africa from growing even larger, highlighting the challenges of containing dangerous infections. In 2020, the World Health Organization (WHO) classified the coronavirus disease 2019 (COVID-19) outbreak as a global pandemic, as it spread to 188 countries and regions throughout that year, causing great social and economic disruption.

Spread of Infectious Diseases

Infectious diseases are either bacterial or viral in nature and spread in different ways. Some, such as smallpox (a virus), are spread through human contact or through material that has come in contact with an infected person. Other diseases, such as influenza (a virus), spread through the air as infected persons cough or sneeze. Bubonic plague (a bacterial disease) is spread to humans through the bites of fleas that have previously bitten infected animals such as rats. (One type of plague—pneumonic plague—is spread through the air from one person to another.) Cholera (a bacterial disease) is spread through drinking water that contains the bacteria Vibrio cholerae. The complicated cycle for the spread of malaria (a protozoal disease) involves an infected mosquito biting a person, as is also the case with yellow fever. HIV/AIDS is a viral disease that spreads through contact with bodily fluids of an infected person.

When the global population was small and disaggregated, it was difficult for infectious diseases to spread because an infected host might never come in contact with a person susceptible to the disease. The growth of urban areas and improved transportation made it possible to spread infectious diseases readily. If a population has no existing immunity or previous exposure to an infectious disease, a so-called virgin-soil epidemic may result if the population is exposed to the disease. When this occurs, the disease may have a high mortality rate and reach pandemic proportions.

Environmental disturbances such as land clearance, construction of lakes, and climate change may affect the spread of infectious diseases by making it easier for microbes to find hosts. Environmental changes may also expose human populations to new diseases by causing mutations in diseases that enable them to spread from animal hosts to humans, as scientists believe occurred with HIV and some of the hemorrhagic fevers.

As medical knowledge improved during the late nineteenth and early twentieth centuries, it became possible for human beings to prevent the spread of many infectious diseases and to treat and cure those who had been infected. Scientists first identify the agent of a disease, such as mosquitoes for yellow fever and malaria, and then look for ways to control the agent, such as draining standing water to decrease the number of mosquitoes. In some cases, it is possible to confer immunity to a disease through vaccination, as occurred with smallpox, which has been eradicated as a disease outside laboratory settings. Other diseases, such as cholera, can be treated with massive rehydration. Malaria can be prevented with the use of chloroquine. A vaccine exists for bubonic plague, and cases can be treated with large doses of antibiotics.

Since the late twentieth century, drug therapy has been successful in preventing many pandemics. Infectious diseases still occur, but in many cases, it is possible for medical personnel to cure such diseases readily and prevent their further spread. However, drug-resistant strains of several diseases, such as malaria and plague, have developed, so that potential for new pandemics exists. HIV/AIDS can be controlled with drug cocktails composed of several drugs, but this viral disease mutates rapidly, so eradication is unlikely. Influenza vaccines exist and are administered every year, but the virus also mutates rapidly, so that new vaccines are necessary for every flu season. In some parts of the world, such as Africa, drug therapies are too expensive for most people; this makes diseases such as HIV/AIDS and cholera difficult to combat, enabling them to reach pandemic proportions. Wars and natural disasters can also produce conditions that encourage the spread of diseases such as cholera.

Historical Overview

Smallpox (caused by the virus Variola major) is one of the oldest infectious diseases; it is known to have existed in antiquity. During the second century BCE what is known as the Antonine Plague saw smallpox spread throughout the Italian peninsula from the Near East. The third century Plague of Cyprian, which may have also been smallpox, led to massive numbers of deaths in Roman Italy. During the American Revolution smallpox broke out in Boston in 1776 and gradually spread across the continent, nearly decimating several of the Native American tribes of the Great Plains.

Plague (Yersinia pestis) is often considered the classic pandemic disease. The first known plague pandemic, the Plague of Justinian, in the sixth century, started in Egypt, and from 541 to 750 bubonic plague spread across the Western world, causing Europe’s population to drop by as much as 50 percent. Possibly originating in Mongolia, plague made another appearance in Europe from 1348 to 1350 and then continued to reappear until the early eighteenth century. The first outbreak, which involved both bubonic and pneumonic plague, killed between 30 and 60 percent of the population in Europe. Combined with other environmental factors, this mortality rate led to a decline in cultivation in some areas and substantially reduced human impacts on the environment.

The third plague pandemic started in western China during the late eighteenth century, spread to coastal cities and India by the late nineteenth century, and reached the United States and South America during the early twentieth century. Although the third plague pandemic did not produce as high a mortality rate as the first two pandemics, it still killed hundreds of thousands of people in China and India. In the early twenty-first century, plague remains endemic in some areas, such as Mongolia and Madagascar, raising the possibility of another major outbreak.

Cholera first appeared as a pandemic disease in the early nineteenth century. The disease had apparently existed in India for some time, but it did not reach the level of a pandemic until 1816–26, when it spread to China, Indonesia, and the Caspian Sea region. Since that time six more cholera pandemics have been recorded. The disease reached England and the United States during the second pandemic (1829–51). The third pandemic (1852–60) mainly affected Russia, Japan, and China, and the fourth (1863–75) affected Europe and Africa. The fifth cholera pandemic (1881–96) was worldwide, causing at least 250,000 deaths in Europe, 50,000 deaths in the Americas, nearly 300,000 deaths in Russia, and 90,000 deaths in Japan. Advances in public health prevented the sixth pandemic (1899–1923) from having much of an impact on Europe or the United States, but as many as 800,000 people died in India and more than 200,000 in the Philippines. The seventh cholera pandemic, which began in 1962 and continues in the early twenty-first century, introduced a new cholera strain, known as El Tor; this pandemic started in Indonesia and spread to India, parts of the former Soviet Union, Africa, and parts of South America.

It is difficult to identify past influenza pandemics because the symptoms are similar to those of many other diseases. An influenza pandemic may have affected most of Europe during the late sixteenth century. A major pandemic that may have caused as many as one million deaths spread worldwide in 1889–90. Some people who contracted the disease and survived had some immunity against influenza during the 1918–19 pandemic, widely known as the Spanish flu, which spread in part due to the large-scale movement of people during World War I. More than 600,000 people died from the disease in the United States, and it has been estimated that 17 million people may have died from the disease in India.

Influenza reached pandemic proportions again in 1957–58 and 1968–69, although it did not produce the large number of deaths that occurred earlier, largely because of improved medical care. Each of these pandemics was caused by a different strain of the influenza virus, which mutates rapidly, making the development of preventive vaccinations difficult. During the early twenty-first century, a new strain of influenza, the H1N1 strain, appeared in China, and by 2009 had spread worldwide. Because of improvements in medical care and preventive measures, influenza during the early twenty-first century does not pose the threat of earlier pandemics. Some researchers, however, have voiced concerns that a new “super-strain” of influenza could occur that will be difficult to treat and will cause a high mortality rate.

HIV, the virus that causes AIDS, may have jumped species from monkeys in Africa sometime during the early twentieth century. By the early 1970s, AIDS was spreading across the globe, and by the 1990s, was increasingly recognized as a major international health threat. By the 2010s, the AIDS pandemic was particularly prominent in Africa, with tens of millions infected with HIV. Some southern and eastern African countries saw considerable declines in population owing to the high mortality rate produced by AIDS as well as related issues. Although HIV/AIDS can be controlled somewhat through drug therapy, this option is expensive and, thus, unavailable to most infected people in Africa and Asia.

The ability of pandemics to manifest rapidly with little warning was apparent with the global outbreak of COVID-19 in 2020. The disease, similar to severe acute respiratory syndrome (SARS), was first diagnosed in Wuhan, China, in December 2019. It is caused by a coronavirus and causes symptoms including fever, headache, muscle ache, fatigue, coughing, sneezing, and difficulty breathing. COVID-19 has no cure and is treated similarly to influenza. The virus is spread by droplets from coughing or sneezing, has a high infection rate, and can last on some surfaces for up to three days. In January 2020 the WHO declared the outbreak of the disease a Public Health Emergency of International Concern, and soon after the status was upgraded to pandemic. By April 2024, 775 million confirmed cases of COVID-19 had spread to virtually every country in the world, causing more than 7 million deaths despite the administration of 5.5 billion vaccine doses.

The Environment and Pandemic Disease

Changes in how human beings relate to the environment have had impacts on the creation and spread of diseases. As humans venture into new environments they encounter new diseases, some of which migrate from other species. In Africa, human-made large lakes helped to spread malaria by providing breeding grounds for the mosquitoes that carry the disease, just as controlling standing water all but eliminated the threat of malaria and yellow fever epidemics in the Western world. Climate change, too, may have an impact on the spread of infectious diseases, as warmer temperatures may make it possible for some tropical diseases to spread to new surroundings.

The high death tolls of some pandemics impacted the environment, although it is difficult to trace these impacts clearly. The high death rate among Native Americans produced by contact with European diseases such as smallpox and even measles seems to have depopulated some areas in the Americas in the sixteenth century. The massive death rates produced by the Black Death (possibly a bubonic plague pandemic) in the fourteenth century substantially decreased the impacts of human activities on the environment. Other pandemics, such as cholera, malaria, and yellow fever, have reduced human populations enough to have produced some environmental impacts. The extremely high number of deaths produced by the influenza pandemic of 1918–19 had little impact on the environment except in isolated regions because of the large size of the world’s population by the early twentieth century. However, the massive economic shutdown caused by COVID-19 in 2020 reduced pollution and increased the presence of wild animals in some areas due to lack of human activity, though these effects were short lived. By 2022, pollution in many areas of the world increased above pre-pandemic levels.

Bibliography

Barnes, Ethne. Diseases and Human Evolution. U of New Mexico P, 2005.

"Coronavirus Disease (COVID-19) Pandemic." World Health Organization, 6 July 2024, www.who.int/emergencies/diseases/novel-coronavirus-2019. Accessed 21 July 2024.

Crawford, Dorothy H. Deadly Companions: How Microbes Shaped Our History. Oxford UP, 2007.

Crosby, Alfred W. America’s Forgotten Pandemic: The Influenza of 1918. 2nd ed. Cambridge UP, 2003.

Engel, Jonathan. The Epidemic: A Global History of AIDS. Smithsonian, 2006.

Fenn, Elizabeth A. Pox Americana: The Great Smallpox Epidemic of 1775–82. Hill, 2001.

McMichael, Tony. Human Frontiers, Environments, and Disease: Past Patterns, Uncertain Futures. Cambridge UP, 2001.

Orent, Wendy. Plague: The Mysterious Past and Terrifying Future of the World’s Most Dangerous Disease. Free, 2004.

Taylor, Derrick Bryson. "A Timeline of the Coronavirus Pandemic." The New York Times, 17 Mar. 2021, www.nytimes.com/article/coronavirus-timeline.html. Accessed 21 July 2024.

Theilmann, John M., and Frances Cate. “A Plague of Plagues: The Problem of Plague Diagnosis in Medieval England.” Journal of Interdisciplinary History, vol. 37, no. 3, 2007, pp. 371-393, www.jstor.org/stable/4139605. Accessed 21 July 2024.