The number of people already infected with the mysterious virus that is emerging in China is far greater than official figures suggest, the scientists told the BBC.
There have been 41 cases confirmed by the laboratory for the new virus, but UK experts estimate that the figure is closer to 1,700.
Two people are known to have died from the virus, which appeared in Wuhan city in December.
“I’m substantially more worried than I was a week ago,” said epidemic scientist Prof Neil Ferguson.
The work was conducted by the MRC Center for Global Analysis of Infectious Diseases at Imperial College London, which provides advice to entities including the UK government and the World Health Organization.
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Singapore and Hong Kong have checked air passengers from Wuhan and U.S. authorities have announced similar measures starting Friday at three major airports in San Francisco, Los Angeles and New York.
How were the numbers calculated?
The crucial clue to the magnitude of the problem lies in the cases found in other countries.
While the outbreak is centered on Wuhan, there have been two cases in Thailand and one in Japan.
“This made me worry,” said prof. Ferguson.
He added: “For Wuhan to export three cases to other countries, this would imply that there should be many more cases than reported.”
It is impossible to get the exact number, but the modeling of epidemics, based on the virus, the local population and flight data, can give an idea.
Wuhan International Airport serves a population of 19 million people, but only 3,400 per day travel abroad.
The detailed calculations, which were published online prior to publication in a scientific journal, produced 1,700 cases.
What does all this mean?
The professor. Ferguson said it was “too early to be alarmist” but was “substantially more concerned” than a week ago.
Chinese officials say there have been no cases of spreading the virus from one person to another.
Instead, they say the virus has crossed the species barrier and comes from infected animals at a seafood and wildlife market in Wuhan.
The professor. Ferguson says, “People should consider the possibility of substantial human-to-human transmission more seriously than they have done so far.
“It would be unlikely in my mind, given what we know about coronaviruses, that exposure to animals is the main cause of such a large number of human infections.”
Understanding how a new virus is spreading is a crucial part of assessing its threat.
What is this virus?
Viral samples were taken from patients and analyzed in the laboratory.
And officials in China and the World Health Organization have concluded that the infection is a coronavirus.
Coronaviruses are a large family of viruses, but only six (the new one would make seven) are known to infect people.
Eventually mild they cause the common cold, but severe acute respiratory syndrome (Sars) is a coronavirus that killed 774 of the 8,098 people infected in an outbreak that started in China in 2002.
Analysis of the genetic code of the new virus shows that it is more closely related to Sars than any other human coronavirus.
The virus caused pneumonia in some patients and was fatal in two of them.
What do other experts say?
Dr Jeremy Farrar, director of the Wellcome medical research charity, said: “There is still much to come from this epidemic.
“Uncertainties and shortcomings remain, but it is clear that there is a certain level of transmission from person to person.
“We are starting to know more cases in China and other countries and it is likely, as this model shows, that there will be many more cases in a number of countries.”
The professor. Jonathan Ball, of the University of Nottingham, said: “What is really important is until widespread laboratory tests have been carried out, it is very difficult to put a real number on the cases in circulation.
“But that’s a figure we should take seriously until we know otherwise, 41 animal-to-human” relapses “are stretching it out a bit and there is probably more underlying infection than has been detected so far.”
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