The coronavirus outbreak that has spread around the world from China since December has sickened more than 105,000 people and killed nearly 3,600.

Most of those who have fallen ill and who have died are from China.

The new coronavirus causes a disease called COVID-19 and has spread from Wuhan, China, to 95 countries as of Sunday morning.

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The World Health Organization says coronaviruses are a large family of viruses that may cause illness in animals or humans.

“In humans, several coronaviruses are known to cause respiratory infections ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS),” WHO says.

“The most recently discovered coronavirus causes coronavirus disease COVID-19.”

Researchers suspect the COVID-19 virus was passed from bats to an intermediate animal source and then to humans, NBC News reports.

SARS emerged in the southern Chinese province of Guangdong in November 2002 before becoming a global epidemic, infecting more than 8,000 people and killing nearly 800 in 26 countries.

WHO says there here have been no outbreaks of SARS anywhere in the world since 2003.

Scientists believe SARS originated in bats that infected civet cats, small mammals that resemble weasels, and then humans.

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WHO says SARS was more deadly but much less infectious than COVID-19.

MERS was first identified in Saudi Arabia in 2012. MERS has been reported in 27 countries since 2012, with approximately 80 percent of human cases reported by the Kingdom of Saudi Arabia.

Cases identified outside the Middle East are of people who were infected while in the Mideast. On rare occasions, small outbreaks have occurred outside that region.

Since 2012 the number of MERS cases has totaled 2,494. More than 850 deaths have been reported.

The virus that causes MERS was found in bats in Saudi Arabia and may have been passed from bats to camels to humans.

Genetic analyses have shown that the coronavirus has not undergone many significant changes since its emergence in Wuhan, according to NBC News. As viruses pass from person to person and spread into new geographical locations, it’s not uncommon for them to mutate to avoid dying out.

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“It’s basically Darwinian evolution, where it’s survival of the fittest,” University of North Carolina epidemiologist Timothy Sheahan told NBC. “But if you already have a virus that is good at human-to-human transmission and good at replicating in a person, there’s no reason for it to get more fit.”