What is a coronavirus? Coronaviruses are a family of viruses that cause disease in animals. Seven, including the new virus, have made the jump to humans but most just cause cold-like symptoms. Two coronaviruses – Middle East respiratory syndrome (Mers) and severe acute respiratory syndrome (Sars) – are much more severe, having killed more than 1,500 people between them since 2002. The new virus, now officially called Covid-19, is also dangerous. So far, around 20 per cent of confirmed cases have been classed as "severe" and the current death rate stands at about two per cent. This is much lower than fatality rates for Mers (30 per cent) and Sars (10 per cent) but still a significant threat. What are the symptoms of coronavirus? For a full read out of the symptoms and treatment of coronavirus click here now. How many people have been affected so far? The new virus is spreading fast and there are nine confirmed cases in the UK. More than 73,000 cases have been confirmed since the outbreak started and the death toll has exceeded 1,800. The vast majority of cases are in China but the virus has spread to 28 other countries. The Philippines was the first country outside China to report a death related from the virus. The Department of Health said a 44-year-old Chinese man from Wuhan was admitted on January 25 after experiencing fever, cough, and sore throat. He developed severe pneumonia and later died. The disease, which causes pneumonia-like symptoms, has forced Beijing to quarantine some 18 major cities, essentially locking down more than 56 million people. What’s the position in the UK? Four more patients in England have tested positive for novel coronavirus, bringing the total number of cases in the UK to eight. The new cases are thought to be linked to a British man who caught the virus at a conference in Singapore and stopped at a ski resort in France before returning to the UK. The patients are currently undergoing treatment at specialist NHS centres at Guy"s and St Thomas" and the Royal Free hospitals in London. Confirming the four new cases on Monday, chief medical officer for England Professor Chris Whitty said they were all "known contacts of a previously confirmed UK case, and the virus was passed on in France". Meanwhile health officials are urgently trying to trace those who came into contact with two patients – who are being treated at Newcastle upon Tyne hospitals NHS foundation trust – after they fell unwell whilst staying in York. Professor Sharon Peacock, director of the National Infection Service at Public Health England (PHE), said: “PHE is contacting people who had close contact with the confirmed cases." Police have been handed unprecedented powers to force those at risk of coronavirus into quarantine, amid fears two GPs may have passed the virus on to their patients. The new measures have been put in place with immediate effect as the health secretary warned that the spread of the virus is now a "serious and imminent threat" to the British public. What about those flown back from Wuhan? After several delays, 83 Britons and 27 non-UK nationals arrived in the UK on a government charter flight from Wuhan on Friday. They were then taken by coach to Arrowe Park hospital in the Wirral for a quarantine period of 14 days, where they will be housed in an NHS staff accommodation block. All are reportedly well. How did the outbreak start? The source of the coronavirus is believed to be a “wet market” in Wuhan which sold a wide variety of both dead and living animals, including fish and birds. Such markets pose a heightened risk of viruses jumping from animals to humans because hygiene standards are difficult to maintain if live animals are being kept and butchered on site. Typically they are also closely packed and very busy places. The animal source of the latest outbreak has not yet been identified but the original host is thought to be bats. Bats were not sold at the Wuhan market but they may have infected live chickens or other animals sold there. Bats are host to a wide range of zoonotic viruses including Ebola, HIV and rabies. Why has the WHO declared an international emergency? The WHO’s primary concern is the virus"s potential to spread unhindered in low and middle income countries, where it could spark a full-blown pandemic. While developed nations like the UK are likely to be able to contain the virus in the short term at least, that is not the case in the poor but globally connected mega-cities of Asia and Africa. The authorities in countries like India, where there have been three confirmed cases, and Kenya, which is investigating suspected cases, have significantly less central control than China and their health systems are rickety at best. The potential for runaway outbreaks in these countries is therefore much greater. Is this virus like Sars and Mers? Yes - but it is nowhere near as lethal. Sars (severe acute respiratory syndrome) and Mers (Middle East respiratory syndrome) are also coronaviruses which cause severe respiratory infections. They also originated in bats, Sars jumping to humans via civet cats and Mers coming via camels. Sars, first reported in China in 2002, spread to 27 countries, infecting around 8,000 people and killing 700. It spread quickly at first but then died out. Mers on the other hand, is more tenacious. It first emerged in 2012 in Jordan and about 2,500 cases of the disease have been identified so far. It is more deadly than Sars, and has claimed about 850 lives in total. How does this coronavirus compare to past respiratory epidemics? The 1918 Spanish Influenza – or the H1N1 virus – remains the most devastating flu pandemic in modern history. The disease swept around the globe and is estimated to have caused between 50 and 100 million deaths. A new version of the same virus was also behind the 2009 swine flu outbreak, which is thought to have killed as many as 575,400 people. Other major influenza outbreaks include the Asian flu in 1957, which led to roughly two million deaths, and the Hong Kong flu 11 years later which killed one million people. But coronavirus outbreaks have so far been far smaller. Sars eventually spread to 27 countries in total, infecting around 8,000 people and killing 700. Is this outbreak likely to become a full-blown global pandemic? It is too early to say. The virus has spread widely in China but even there the total numbers remain relatively small compared to the country’s 1.4 billion population. It has jumped to more than 20 other countries, including the UK, but so far there is little evidence of the virus spreading in a sustained manner outside of China. The WHO says it is not yet a pandemic as the majority of cases in other countries have been imported from China. Is there anything I should be doing to prepare? Yes, there are plenty of basic precautions you can take to protect yourself against catching respiratory viruses of this type. Click here now for a full briefing on the symptoms, treatments and precautions you can take against the new coronavirus. Protect yourself and your family by learning more about Global Health Security. And sign up to our weekly newsletter here.