Definitions
An epidemic is a contagious, infectious, or viral disease
affecting a disproportionate number of persons in a community, region, or
population at the same time. A pandemic is a contagious, infectious,
or viral disease occurring over a large geographical area or affecting a high
proportion of a certain population.
Although both the terms "epidemic" and "pandemic" refer to a disease spreading through a population, a pandemic usually indicates either a larger geographical area or a higher number of people affected, or sometimes both. For example, a disease, such as influenza, may occur in a limited geographical area in many more people than would be expected. However, if the disease never spreads widely (perhaps only a few other cases appear nationwide), this situation would be an epidemic. However, if the disease spreads into a larger geographical area, for example, across an entire continent, with many more people contracting the disease than would be expected, this episode would then be termed a pandemic.
Another use of the term "pandemic" occurs when the disease affects an inordinate amount of people in a localized population. For example, in some areas of Africa, nearly 100 percent of the population may be infected with the human immunodeficiency virus (HIV), making the situation a pandemic. Generally, a pandemic starts as an epidemic that, because of poor management, negligence, or ignorance, spreads into a larger area or affects a larger percentage of a population.
The application of the words "epidemic" and "pandemic" also depends on what is expected or what has been experienced in the past. For example, the common cold is a virus that is experienced worldwide; however, it is expected and it is known, from experience, that many people contract the virus that leads to the common cold. Even though the cold is a widespread illness, it is not a pandemic, or even an epidemic. However, hantavirus infection, being very rare and neither expected nor experienced by many, becomes epidemic when a few people do become infected.
The words "epidemic" and "pandemic" are also often used in connection with diseases or conditions, such as diabetes or obesity, that are not infectious. In their true scientific senses, epidemic and pandemic refer only to conditions that are contagious or transmittable from one person to another.
Causes
Disease epidemics have been recorded since at least the time of the pharaohs in ancient Egypt, and there are biblical references to plagues and diseases that spread rapidly and decimated human populations. Some of the most striking examples of past epidemics and pandemics include the Black Death, an outbreak of bubonic plague that spread through Europe in the fourteenth century; the smallpox epidemic that affected Native Americans at first contact with Europeans in the New World; and the Spanish flu, a form of influenza that spread around the world in 1918, killing millions of people in just eighteen months.
Epidemics can be spread by many different means, including by an infectious carrier, contamination, mutation of an infectious agent, human behavior, and environmental change.
Infectious carrier. Sometimes animals carry disease that can spread rapidly through a population. For example, the bubonic plague, which killed an estimated one of every four people in Europe and one of every two people in Venice alone in 1347–1348, is thought to have been spread by rats carrying fleas infected with the disease. These fleas easily made the transition from being carried by rats to being carried by people, and through their bites, the fleas spread this disease. Other examples of vectors (organisms that carry disease) are the ticks that carry Lyme disease.
It is also possible for a person to be a vector, to carry a disease without
becoming or being infected. These carriers can infect others unknowingly.
For example, in the early twentieth century case of Mary Mallon
(also known as Typhoid Mary), who worked as a cook, Mallon infected more than
forty people with typhoid fever. She was immune to typhoid, even though she
carried the disease.
Contamination. Contamination of water or food can also be a source of epidemics, such as cholera, which is transmitted through contaminated water. Strange cases of outbreaks can be tied to contamination. For example, an outbreak of cases involving
Salmonella
bacteria in Minnesota in 1994 was traced back to a particular brand of ice cream. However, Salmonella can be found only in poultry and eggs. Because the ice cream contained neither, the outbreak was puzzling. Further investigation revealed that the ice cream was created with a mix that had been carried by trucks that had previously carried unpasteurized eggs. Another factor was inadequate cleaning, which had contaminated the ice cream mix.
Mutation of an infectious agent. Even when the infectious agent is known, as are the
Plasmodium
microbes that cause malaria, an agent’s ability to quickly mutate to survive can foil attempts to prevent the spread of disease. These microbes reproduce so rapidly and change genetic material so often that it is difficult for malarial medicine to keep up with the changes. Another problem that continues the spread of malaria is that involving the mosquitoes that carry the disease; they too can quickly mutate and thus survive the application of pesticides, making it difficult to control the population of the infected vectors.
Human behavior. Social and political issues also affect how disease is spread. For example, even though many studies have shown that the best way to prevent the spreading of disease is frequent handwashing, other studies show that people do not always comply with handwashing recommendations. Another example is the refusal by some parents to vaccinate their children against diseases, even though the benefits of immunization and vaccination far outweigh the risks. Also, sexual contact can transmit infectious diseases; some people refuse to practice safer sex, even though doing so has been proven to reduce sexually transmitted diseases (STDs). Lack of education and access to medications are other issues that allow disease to spread.
Another factor in the spread of disease is the introduction of new diseases by nonindigenous populations. For example Native Americans had contact with early settling Europeans, who had gained immunity to but still carried infectious agents, causing Native Americans—who had never been exposed to the smallpox virus and thus had no opportunity to develop immunity to it—to contract severe and oftentimes fatal infections from their first exposure. This type of disease transmission still occurs today. With more people traveling the globe, diseases are spread more quickly among populations; for example, severe acute respiratory syndrome (SARS) spread rapidly throughout the world in early 2003 because of the high number of international travelers who were infected.
Political issues also interfere with disease control. US president Woodrow Wilson was roundly criticized for his policies during the influenza outbreak of 1918. Even though many people were dying from influenza, he refused to move resources focused on fighting in World War I to fighting the disease, thus possibly contributing to the spread of the disease and to many more deaths. Poor domestic health services and ineffective response coordination contributed to the epidemic of ebola hemorrhagic fever in several West African countries beginning in 2013; the complications of international politics also delayed efforts to contain the disease.
Environmental change. A short-term or long-term change in environmental conditions can contribute to the spread of a disease. An example of environmental change contributing to an epidemic is that of the hantavirus. This virus mysteriously appeared in Native Americans in the American Southwest in 1993, infecting three healthy people and rapidly killing them. The virus then spread through the population.
Through a series of investigations, epidemiologists discovered that after years of drought, a snowy winter and wet spring had led to an increase in pinion nuts in the area, which, in turn, led to an increase in mice that ate these nuts. The hantavirus can be carried in the feces and urine of these mice. Infection occurred when people cleaned up the mouse droppings, inhaled the virus that was in the contaminated dust, and then passed the virus to other humans. Because of the change in weather, the mice, who had always been in the area, increased in numbers. This led to greater contact with the human population.
Environmental change contributed to the spread of disease among the people of
the Lyme, Connecticut, area. People began building homes farther into the woods,
which led to more contact with deer that were native to the area. These deer
carried ticks that, in turn, carried the bacterium Borrelia
burgdorferi. When the ticks began to leave their deer hosts and to
infect humans with this bacterium, humans contracted what came to be called
Lyme
disease.
Management
Seventeenth century Dutch scientist Antoni van Leeuwenhoek first looked into his microscope and saw "little animals," thus inspiring scientists such as Robert Koch and Louis Pasteur to study and understand that microbes can cause diseases that can be transmitted from one person to another. Scientists still work at creating antibacterials, antivirals, and vaccines that will prevent people from getting or spreading disease.
However, even with all the medications that are available, there are other hurdles to overcome in managing diseases. Often, medications are too expensive, or, as in cases of war or other civil disruptions, medications do not get to those who need them. Also, a decline in sanitary conditions can lead to outbreaks of disease. Vaccination programs can fail to reach a critical mass of people to keep infectious diseases under control.
Public health agencies also have a role to play in managing disease. John
Snow had been credited with the first public health action in
managing the spread of disease after he investigated the London cholera outbreak
in 1854. Cholera was raging through the city, and many still believed that disease
was caused by bad air or humours. Snow, however, plotted the cholera outbreak by
using a map to pinpoint the cases of the disease. He noticed that many of the
people with the disease were getting water from the Thames River through a pump;
the river, at the time, was severely polluted with human waste. Even though he
made his findings public, some people refused to believe that the polluted water
was causing their illnesses. The Reverend Harry Whitehead found Snow’s evidence
compelling and worked with Snow to convince city officials to remove the handle of
the pump, rendering it unusable. This public health intervention led to a rapid
decline in the cases of cholera in the area and to an overhaul and general cleanup
of London water sources.
These types of outbreaks still occur, and public health officials resort to seemingly drastic measures to try to control the spread of disease. For example, during a cryptosporidium outbreak in 2007, public health officials in Utah intervened to ensure public safety by asking that children younger than age five years, persons wearing a diaper, and persons with diarrhea avoid using public swimming pools. Even after the outbreak subsided, small children were required to wear a swim diaper and plastic pants to help curb the disease.
Impact
Epidemics have raged through populations since the beginning of human existence, and the future will be no different. The ability of infectious agents to propagate and mutate far outstrips the human immune system’s ability to adapt to and fight contagious diseases. However, fear and ignorance of how disease is transmitted have a huge societal and economic impact. For example, misunderstandings of how a particular disease is transmitted led to fear of touching persons with AIDS at the beginning of the AIDS pandemic. More recently, misunderstandings of how the H1N1 virus is transmitted led to the slaughter of pigs in certain countries. Neither of these actions impacted the infection rates of these diseases.
The keys to preventing epidemics and pandemics include
understanding how a particular disease is transmitted and spread through a
population; using public health pathways to provide and act upon scientifically
proven information, both in controlling a disease and preventing it in the first
place; and educating the public on good health practices, both socially and
physically.
Bibliography
Baker, Robert. Epidemic: The Past, Present, and Future of the Diseases that Made Us. London: Vision, 2008. Print.
Barry, John M. The Great Influenza: The Story of the Deadliest Pandemic in History. New York: Penguin Books, 2005. Print.
Bisen, Prakash S., and Ruchika Raghuvanshi. Emerging Epidemics: Management and Control. Hoboken: Wiley, 2013. Print.
DeSalle, Rob, ed. Epidemic! The World of Infectious Disease. New York: New Press, 2000. Print.
Doherty, P. C. Pandemics. Oxford: Oxford UP, 2013. Print.
Giles-Vernick, Tamara, and Susan Craddock, eds. Influenza and Public Health: Learning from Past Pandemics. London: Earthscan, 2010. Print.
Hardt, Mark D. History of Infectious Disease Pandemics in Urban Societies. Lanham: Lexington, 2015. Print.
Herring, Ann, and Alan C. Swedlund. Plagues and Epidemics: Infected Spaces Past and Present. New York: Berg, 2010. Print.
Johnson, Steven. The Ghost Map: The Story of London’s Most Terrifying Epidemic, and How It Changed Science, Cities, and the Modern World. New York: Riverhead Books, 2007. Print.
McKenna, Maryn. Beating Back the Devil: On the Front Lines with the Disease Detectives of the Epidemic Intelligence Service. New York: Free Press, 2008. Print.
Moore, Peter. Little Book of Pandemics. New York: Harper, 2008. Print.
Pendergrast, Mark. Inside the Outbreaks: The Elite Medical Detectives of the Epidemic Intelligence Service. Boston: Houghton Mifflin Harcourt, 2010. Print.
No comments:
Post a Comment