A virus – previously unknown to science – is causing severe lung disease in China and has also been detected in other countries.
Scores of people are known to have died from the virus, which appeared in the Chinese city of Wuhan in December, last year. There are already hundreds of confirmed cases, and experts expect the number will keep rising.
These are a broad family of viruses, but only six (the new one would make it seven) are known to infect people.
The symptoms start with a fever, followed by a dry cough and then, after a week, leads to shortness of breath and some patients needing hospital treatment. Around one-in-four cases are thought to be severe.
The coronavirus family itself can cause symptoms ranging from a mild cold all the way through to death.
“When we see a new coronavirus, we want to know how severe are the symptoms. This is more than cold-like symptoms and that is a concern but it is not as severe as Sars,” says Prof Mark Woolhouse, from the University of Edinburgh.
The World Health Organization (WHO) could consider declaring an international public health emergency – as it did with swine flu and Ebola.
At least 56 people are known to have died from the virus – but while the ratio of deaths to known cases appears low, the figures are unreliable. But the infection seems to take a while to kill, so more of those patients may yet die. And it is unclear how many unreported cases there are.
Severe Acute Respiratory Syndrome (SARS):
Severe acute respiratory syndrome (Sars), which is caused by a coronavirus, killed 774 of the 8,098 people infected in an outbreak that started in China in 2002.
“There is a strong memory of Sars, that’s where a lot of fear comes from, but we’re a lot more prepared to deal with those types of diseases,” says Dr Josie Golding, from the Wellcome Trust.
Sars started off in bats and then infected the civet cat, which in turn passed it on to humans.
Middle East respiratory syndrome (MERS):
Another virus, Middle East respiratory syndrome (Mers), which has killed 858 out of the 2,494 recorded cases since it emerged in 2012, regularly makes the jump from the dromedary camel.
Once the animal reservoir (where the virus normally camps out) is detected, then the problem becomes much easier to deal with.
The coronavirus cases have been linked to the South China Seafood Wholesale Market, in Wuhan.
But while some sea-going mammals can carry coronaviruses (such as the Beluga whale), the market also has live wild animals, including chickens, bats, rabbits, snakes, which are more likely to be the source. Researchers say the new virus is closely related to one found in Chinese horseshoe bats.
At the beginning of the outbreak, the Chinese authorities said the virus was not spreading between people – but now, such cases have been identified.
Scientists have now revealed each infected person is passing the virus on to between 1.4 and 2.5 people. This figure is called the virus’ basic reproduction number – anything higher than 1 means it’s self-sustaining. We now know this is not a virus that will burn out on its own and disappear.
Only the decisions being made in China – including shutting down cities – can stop it spreading.
While those figures are early estimates, they put coronavirus in roughly the same league as Sars. There are also concerns that people with no symptoms could be spreading the virus. It might appear as though cases have soared, from 40 to more than 800 in around a week. But this is misleading.
Most of the “new” cases were already out there but have only just been detected as China steps up its surveillance.
There is actually very little information on the “growth rate” of the outbreak. But experts say the number of people becoming sick is likely to be far higher than the reported figures.
A report by the MRC Centre for Global Infectious Disease Analysis at Imperial College London put the number of cases to 4000.
While the outbreak is centred on Wuhan, there have been cases in Thailand, Japan, South Korea, Vietnam, France, Singapore, Taiwan, Nepal and the US.
At the moment there is no vaccine or treatment available for the virus. However, the work to develop them is already under way. It could take a minimum of six months before a vaccine hits the markets.