Since it's discovery in December 2019, the coronavirus sweeping the globe has infected more than 400,000 people worldwide.

It's been detected in nearly every country, and COVID-19, the respiratory disease caused by coronavirus, has killed more than 18,000 people to date.

The rapid rate of transmission has prompted countries to lock down travel and borders, cripple the economy, force businesses and schools to close and overload health care systems.

Infectious disease experts warn people to practice "social distancing," or remaining at least 6 feet away from others, in an attempt to "flatten the curve." These phrases quickly have become part of a new lexicon for most people.

The novel coronavirus, though, is just one of many pandemics that have arrived with little warning. For centuries, virus outbreaks have swept across the globe, killing millions of people.

Here is a look at the world's most deadly pandemics.

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