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A virus – previously unknown to science – is causing severe lung disease in China and has also been detected in other countries.
At least 200 people are known to have died from the virus in China, which appeared in the city of Wuhan in December, with around 10,000 cases nationally.
There have also been cases 22 countries, including in the UK, but no deaths.
Experts expect the number will keep rising.
A new virus arriving on the scene, leaving patients with pneumonia, is always a worry and health officials around the World Health Organization has declared a global emergency.
Can this outbreak be contained or is this something far more dangerous?
Science What is this virus?
Officials in China have confirmed the cases are caused by a coronavirus.
These are a broad family of viruses, but only six (the new one would make it seven) are known to infect people.
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.
Science How severe are the symptoms?
It seems to 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-five cases are thought to be severe.
Notably, the infection rarely seems to cause a runny nose or sneezing.
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.
Science How deadly is it?
While the ratio of deaths to known cases appears low, the figures are unreliable.
It is far too simplistic to divide the number of deaths by the number of cases to calculate the death rate to get a figure of around 2% at this stage of the outbreak.
Thousands of patients are still being treated and we do not know if any of those cases will die – so the death rate could be higher.
And it is unclear how many unreported cases there are – so the death rate could be lower.
Science Where has it come from?
New viruses are detected all the time.
They jump from one species, where they went unnoticed, into humans.
“If we think about outbreaks in the past, if it is a new coronavirus, it will have come from an animal reservoir,” says Prof Jonathan Ball, a virologist at the University of Nottingham.
Many of the early coronavirus cases were linked to the South China Seafood Wholesale Market, in Wuhan.
But the earliest documented case, which has been traced back to 1 December, had no connection to the market.
Sars started off in bats and then infected the civet cat, which in turn passed it on to humans.
And 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.
Science Which animal?
Once the animal reservoir (where the virus normally camps out) is detected, then the problem may become easier to deal with.
While some sea-going mammals can carry coronaviruses (such as the Beluga whale), the South China Seafood Wholesale Market also has live wild animals, including chickens, bats, rabbits, snakes, which are more likely to be the source.
The new virus is closely related to one found in Chinese horseshoe bats.
However, this does not mean wild bats are the source of the outbreak – they could have passed the virus onto another species sold at the market.
Science Why China?
Prof Woolhouse says it is because of the size and density of the population and close contact with animals harbouring viruses.
“No-one is surprised the next outbreak is in China or that part of the world,” he says.
Science How easily does it spread between people?
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 say each infected person is passing the virus on to between two and three people.
This figure is called the virus’ basic reproduction number – anything higher than 1 means it’s self-sustaining.
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.
Those figures are constantly being revised, but put the novel coronavirus in roughly the same league as Sars.
Science When are people infectious?
Chinese scientists say people are infectious even before their symptoms appear.
The time between infection and symptoms – known as the incubation period – lasts up to 14 days.
Sars and Ebola are contagious only when symptoms appear. Such outbreaks are relatively easy to stop: identify and isolate people who are sick and monitor anyone they came into contact with.
Flu, however, is the most famous example of a virus that you spread before you even know you’re ill.
Prof Wendy Barclay from the department of infectious disease at Imperial College London said it was common for lung infections to spread without symptoms.
The virus is “carried into the air during normal breathing and talking by the infected person,” she explained.
“It would not be too surprising if the new coronavirus also does this.”
We are not at the stage where people are saying this could be a global pandemic like swine flu.
But the problems of stopping such “symptomless spreaders” will make the job of the Chinese authorities much harder.
What is not known is how infectious people are during the incubation period.
Science How fast is it spreading?
It might appear as though cases have soared. But this is somewhat misleading.
Many of these seeming new cases will have come to light as a result of China improving its ability to find infected people.
Estimates by the University of Hong Kong suggest the true total number of cases could be far higher than official figures suggest.
Their mathematical models of the outbreak suggest more than 75,000 people may have been infected in the Chinese city of Wuhan alone.
Multiple groups have estimated the number of cases is doubling every week.
Science Why a global emergency?
The World Health Organization (WHO) says the virus is a, public health emergency of international concern – as it did with swine flu and Ebola.
It said it has done so in order to provide extra support to lower and middle-income countries with weaker health systems that might not be able to spot or isolate cases of coronavirus.
Science Could the virus mutate?
Yes, you would expect viruses to mutate and evolve all the time. But what this means is harder to tell.
China’s National Health Commission has warned the coronavirus’s transmission ability is getting stronger, but they were unclear on the risks posed by mutations of the virus.
This is something scientists will be watching closely.
Science How can the outbreak be stopped?
We now know the virus will not stop on its own; only the actions of the Chinese authorities can bring this epidemic to an end.
The only option is to prevent people who have become infected from spreading the virus to others.
- limiting people’s movement
- encouraging hand-washing and other forms of infection control
- treating patients in isolation with healthcare workers wearing protective gear
A massive feat of detective work will also be needed to identify people whom patients have come into contact with to see if they have the virus.
Science Are there any vaccines or treatments?
However, the work to develop them is already under way. It is hoped that research into developing a vaccine for Mers, which is also a coronavirus, will make this an easier job.
And hospitals are testing anti-viral drugs to see if they have an impact.
A combination of two drugs – lopinavir and ritonavir – was successful in the Sars epidemic and is being tested in China during this outbreak.
Treatment at the moment relies on the basics.
Patients are kept in isolation so they do not spread the virus; breathing support is given to people with the worst lung disease; and doctors manage the other conditions the patients have.
Science How have Chinese authorities responded so far?
China has done something unprecedented anywhere in the world – by effectively putting entire cities into quarantine.
The central province of Hubei, where nearly all deaths have occurred, is in a state of lockdown.
The province of 60 million people is home to Wuhan, the heart of the outbreak.
The city has effectively been sealed off and China has put numerous transport restrictions in place to curb the spread of the virus.
Some mass gatherings have been banned and tourists sites, including part of the Great Wall, have been closed.
And a ban on the sale of wildlife, a possible source of the infection, has been imposed.
Wuhan – the centre of the outbreak – is building two new hospitals with beds for a total of 2,300 people.
Science How worried are the experts?
Dr Golding says: “At the moment, until we have more information, it’s really hard to know how worried we should be.
“Until we have confirmation of the source, that’s always going to make us uneasy.”
Prof Ball says: “We should be worried about any virus that explores humans for the first time, because it’s overcome the first major barrier.
“Once inside a [human] cell and replicating, it can start to generate mutations that could allow it to spread more efficiently and become more dangerous.
“You don’t want to give the virus the opportunity.”
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