What is the coronavirus and how worried should we be?

What are the symptoms, how is it transmitted from one person to another, and how is the virus from Wuhan in China related to Sars?

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It is a novel coronavirus - that is to say, a member of the coronavirus family that has never been encountered before. Like other coronaviruses, it has come from animals. Many of those infected either worked or frequently shopped in the Huanan seafood wholesale market in the centre of the Chinese city, which also sold live and newly slaughtered animals. New and troubling viruses usually originate in animal hosts. Ebola and flu are examples.