A timeline of Covid-19 as the number of confirmed cases increases around the world.
Covid-19 could have spread among humans for years or even decades before now, a team of scientists has discovered in an alarming new development.
The virus may have jumped from animals to humans long before the first detection in Wuhan, according to research by an international team of scientists.
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Researchers from Australia, Britain and the US sought clues about the disease's past and found it might have jumped from animal to humans long before the first detection in the central China city of Wuhan. In fact, these scientists have speculated that it could have been as long as a decade.
The study was released on March 17 in the scientific journal Nature Medicine.
It was conducted by Kristian Andersen from the Scripps Research Institute in California, Andrew Rambaut from the University of Edinburgh in Scotland, Ian Lipkin from Columbia University in New York, Edward Holmes from the University of Sydney, and Robert Garry from Tulane University in New Orleans.
Dr Francis Collins, director of the US National Institute of Health, said the study suggested that coronavirus had crossed from animals to humans long before it became capable of causing disease in people.
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"Then, as a result of gradual evolutionary changes over years or perhaps decades. The virus eventually gained the ability to spread from human to human and cause serious, often life-threatening disease," he said in an article published on the institute's website on Thursday.
They're not the only scientists to notice the trend.
Italian professor Giuseppe Remuzzi has noticed "strange pneumonias" in Italy since last November, which means the virus could have reached Europe before anyone knew about it.
Prof Remuzzi, director of the Mario Negri Institute for Pharmacological Research in Milan, said he would not be surprised if some asymptomatic carriers had travelled around China or even abroad earlier than December.
He said the unusual cases of pneumonia in November and December could mean that virus was already circulating in Lombardy, Italy's worst-hit region, before people were aware of what was unfolding in Wuhan.
A Beijing doctor working in a public hospital treating COVID-19 patients said numerous cases of mysterious pneumonia outbreaks had been reported by health professionals in several countries last year.
"There will be a day when the whole thing comes to light," said the doctor, who did not want to be named.
In December, doctors in Wuhan began noticing a surge in the number of people suffering from a mysterious pneumonia.
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Tests for flu and other pathogens returned negative.
An unknown strain was isolated, and a team from the Wuhan Institute of Virology led by Shi Zhengli traced its origin to a bat virus found in a mountain cave close to the China-Myanmar border.
