Pandemics: Definition, History & Examples

Instructor: Shannon Compton

Shannon teaches Microbiology and has a Master's and a PhD in Biomedical Science. She also researches cancer and neurodegenerative diseases.

The Bubonic Plague and the Black Death are two famous diseases we classify as pandemics. But what is a pandemic? How do we know if the flu season we are having is just a really bad flu, or a pandemic? This lesson will define them and give examples.

Pandemics Defined

Microscopic view of a virus and bacteria
Microscopic view of a virus and bacteria

If you're searching for the definition of a pandemic, a good place to look is with an official of the World Health Organization (WHO). According to Dr. Keiji Fukuda, Assistant Director-General ad Interim for Health Security and Environment, 'An easy way to think about pandemic ... is to say: a pandemic is a global outbreak. Then you might ask yourself: 'What is a global outbreak'? Global outbreak means that we see both spread of the agent ... and then we see disease activities in addition to the spread of the virus.'

According to the above definition, for a disease outbreak to be considered a pandemic it must fit two criteria. First, it must be global. This means it must spread from one country to another. Second, disease activity is seen in areas with the virus. Disease activity is when a person infected with a disease shows symptoms.

Other important factors when considering a pandemic include virulence and mortality. Virulence is defined as how well the disease infects a person and how sick an infected person gets. A disease that only infects people whose immune system is weakened is less virulent than a disease that infects everyone it contacts. Also, a disease that makes you feel a bit achy and nauseated for a few days is less virulent than one that makes you sick for weeks with a fever and nausea. Mortality is defined as how many people die after catching the disease.

Famous Pandemics in History

Some of the following examples of historical pandemics were caused by a virus and some by a bacterium. In all cases they spread worldwide, were highly virulent, and had high mortality rates.

The Triumph of Death by Pieter Bruegel
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The Black Death is considered to be one of the most deadly pandemics in history. It began in the 14th century and killed about 75 to 200 million people worldwide. There have been several epidemics of bubonic plague since the Black Death, with the last occurring in the 18th century. The bubonic plague is caused by a bacterium which infects rat fleas. People get the disease when they are bitten by an infected rat flea.

Cholera is also a bacterium. It is spread by eating or drinking food or water that has been contaminated by feces from someone with cholera. Cholera outbreaks have caused seven major pandemics. The first pandemic started in 1816 and killed about 2 million people. The last pandemic spanned the years 1962 - 1975. This outbreak killed almost 600,000 people.

The Influenza pandemics are perhaps some of the most famous. The first occurred in 1580, and they reoccur every 30 to 50 years. There have been 4 major flu pandemics. They are the Russian Flu (1889-1890, 1 million deaths), the Spanish Flu (1918-1919, 68 million deaths), the Asian Flu (1957-1958, 2 million deaths), and the Hong Kong Flu (1968-1969, 1 million deaths).

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