Wikipedia defines a pandemic as an epidemic of infectious disease that is spreading through human populations across a large region; for instance a continent, or even worldwide.

But a widespread infectious disease that is stable in terms of how many people are getting sick from it is not a pandemic. A pandemic differs from an epidemic in that a pandemic is more serious and covers a wider region than an epidemic.

Most recent, the bird flu (Influenza A virus subtype H5N1, A(H5N1) or simply H5N) has been currently perceived as a significant emerging pandemic threat. There are countless instances of mass pandemics in history, and some have even been powerful enough to topple governments and nearly wipe out whole civilizations.

Malaria, currently one of the world’s most devastating pandemics, infects as many as 500 million people every year. The malaria parasite is resistant to some drugs, with no dependable vaccine developed yet. It is now mostly confined to the Tropics.

Typhus, known for its ability to spread quickly in cramped and unsanitary conditions, caused millions of deaths in the 20th century. About 8 million Germans were killed by a Typhus pandemic during the 30 years war. It was also a significant cause of death in the Nazi concentration camps. 

Typhus is more famously known for nearly wiping out the French army during Napoleon’s invasion of Russia. It is estimated that about as many as 400,000 of his soldiers may have died from the disease, many more than were killed in combat.

The Cholera pandemic is one of the most consistently dangerous diseases in history. Cholera killed millions between 1816 and the early 1960s. Generally transmitted through contaminated food or drinking water, the disease first sprang up in India, where it is said to have killed as many as 40 million between 1817 and 1860.

It would soon spread to Western Europe and the United States, where it killed more than a 100,000 people in the mid-1800s. Since then, there have been periodic outbreaks of cholera, but advances in medicine have made it a much less deadly disease. Its mortality rate has been reduced from over 50% to death only in the rarest of circumstances.

Smallpox devastated the Americas when European settlers first introduced it in the 15th century. It is credited with the deaths of millions of native peoples in the United States and Central America. Smallpox decimated the Aztec and Incan civilizations and is generally considered to be a major factor in their eventual conquering by the Spanish.

The disease was equally dangerous back in Europe, where it is estimated to have killed 60 million people in just the 18th century alone.

Arriving just after the devastation of World War I, the Spanish Flu of 1918 is widely considered to be one of the most vicious pandemics in history. A worldwide disaster, it is estimated to have infected one third of the world’s entire population, and eventually killed as many as 100 million people.

The virus, which has since been identified as a strain of H1N1, would surface in waves, frequently disappearing in communities as quickly as it arrived. Fearing a massive uproar, governments did their best to downplay the severity of the flu, and because of wartime censorship, its far-reaching effects were not fully realized until years later. Only Spain, a neutral country during WWI, allowed comprehensive news reporting on the pandemic, which is why it eventually became known as the Spanish Flu.

The Black Death is perhaps the most well known pandemic in history. It was a massive outbreak of bubonic plague that ravaged Europe through most of the 1300s. Characterized by the appearance of oozing and bleeding sores on the body and a high fever, the plague is estimated to have killed anywhere from 75 to 200 million people in the 14th century alone, with recent research concluding that 45-50% of the entire population of Europe was wiped out.

The Plague remained a constant threat for the next 100 years, periodically resurfacing and killing thousands, with the last major outbreak occurring in London in the 1600s.

There have been other deadly pandemic that have ravaged societies. Most notable of these are;

The Plague of Justinian (541 AD, killed over 100 million people worldwide–5,000 people a day at its peak). The Plague of Athens (430 BC, killed a third of the total population of Greece).The Third Pandemic (Bubonic plague (1850-1950), following the Plague of Justinian and the Black Death. Killed about 12million people)

But what is right now terrorizing the world is the HIV/AIDS pandemic. First detected around 1969, HIV, the virus that causes AIDS, is currently a pandemic, with infection rates as high as 25% in some parts of southern and eastern Africa.

In 2006 the HIV prevalence rate among pregnant women in South Africa was 29.1%. Effective education about safer sexual practices and bloodborne infection precautions training have helped to slow down infection rates in several African countries.

AIDS could kill 31 million people in India and 18 million in China by 2025, according to projections by U.N. AIDS death toll in Africa may reach 90-100 million by 2025.  
 
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