A new strain of coronavirus — named 2019-nCoV — has been discovered in China. Viruses in the coronavirus category can cause fever, breathing difficulties, pneumonia and diarrhea. Some are potentially fatal. Others can cause the relatively mild common cold.

Here is a look at the most well-known coronaviruses: what they have in common and how they differ.

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The word “corona” is Latin for crown. Under a microscope, these viruses look like a circle with spikes ending in little blobs coming off the surface. Treatment for the more severe coronaviruses typically consists of rest, quarantine and/or hospitalization. There are no approved vaccines at this time.

Currently, there are many unknowns about what is informally referred to as “Wuhan coronavirus,” for the city where cases were first diagnosed. Among the questions being investigated: how the disease is transmitted and how lethal it is.

“Whenever a virus enters the human population from animals, we don’t know its full potential at that time,” says David Heymann, an epidemiologist at the London School of Hygiene & Tropical Medicine.

And different viruses in this category have different impacts. “SARS [severe acute respiratory syndrome] killed people of all ages. It was a very vicious and very violent virus infection,” says Heymann. “MERS [Middle East respiratory syndrome], however, doesn’t appear to be so virulent in younger people.”

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