The World Health Organization (WHO) defines key terms used in the discussion of pandemic diseases: "A disease epidemic occurs when there are more cases of that disease than normal. A pandemic is a worldwide epidemic of a disease." Scientific research has assisted in eradicating diseases that created pandemics in earlier generations, but the threat of new pandemics increases in an age where large numbers of people travel the continents quickly by air.
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The Centers for Disease Control defines the plague as "...an infectious disease of animals and humans caused by a bacterium named 'Yersinia pestis.'" The plague, transferred by fleas hiding on goods and people traveling from region to region, killed millions of people during the Middle Ages. The CDC notes that the plague continues to infect people living in rural and remote areas. The last major urban epidemic occurred in Los Angeles during the mid-1920s. Campgrounds are routinely closed today due to plague infestations of squirrels and rodents. As of 2009, the disease is controlled by early dosages of antibiotics.
Tuberculosis (TB) was the leading cause of world death after World War I, with returning troops serving as carriers of the pandemic disease. TB is caused by "...a bacterium called 'Mycobacterium tuberculosis,'" according to the CDC. It can attack any part of the body, but the lungs are infected in most patients. TB is spread by breathing in bacteria from an infected person. Current outbreaks of the disease involve a virulent, mutated strain typed "XDR-TB" that is resistant to modern drugs (the "DR" designation stands for "drug resistant").
Polio was a pandemic disease in the 1950s. Due to a subsequent world effort, it was considered eradicated until the 1980s when countries ceased immunizing children against the disease. WHO's efforts to bring polio under control have reduced the number of cases from 350,000 in 1988 to less than 1,200 in 2005. The clear lesson is that constant medical vigilance is necessary to prevent pandemic outbreaks from reoccurring.
The influenza (flu) pandemics of 1918 and the 1950s killed millions of people. WHO estimates more than 40 million died in the 1918 to 1919 outbreak alone and speculates that more than seven million may die in a contemporary flu pandemic. WHO, the U.S. Centers for Disease Control (CDC), heads of world government, and corporate and non-profit agencies work together each year to develop flu vaccines to slow the spread of the disease.
Any disease has the potential to become a pandemic if treatment is delayed and it is transferred from the host geographic region to other areas. The Voice of America (VOA) lists Ebola Hemorrhagic Fever and AIDS as potential 21st century pandemics. Influenza, TB and severe acute respiratory syndrome (SARS), diseases that impacted the world as pandemics from the past, also top the VOA list for future pandemics.