THE number of people infected with a mystery lung disease - previously unknown to science - tripled over the weekend, with the outbreak spreading across China and global concern growing.

What is it?

The virus has been labelled 019-nCoV and is understood to be a new strain of coronaviruses (CoV), not previously seen in humans.

CoVs are a “broad family of viruses”, according to the World Health Organisation (WHO), but only six were known to infect humans, so this would be the seventh.

When did the first case appear?

It was identified by the WHO at the end of December after several cases of apparent pneumonia were detected in Wuhan City, Hubei Province of China.

Where has it come from?

Scientists believe it is most likely to have come from an animal source - preliminary WHO investigations identified environmental samples positive for the disease in Huanan Seafood Wholesale Market in Wuhan City. Experts believe, though, that it is the other wild animals at the market, including bats, rabbits, snakes and chickens, that are more likely to be the cause, rather than seafood.

How does it affect people?

Signs of infection include respiratory symptoms, fever, cough, shortness of breath and breathing difficulties.

It’s connected to SARS?

Analysis of SARS - a CoV that killed nearly 800 of 8,000 infected in an outbreak that began in China in 2002 - shows that the new virus is closely related to it.

It’s spreading rapidly?

In Wuhan, which has a population of more than 11 million, 136 new cases were confirmed at the weekend, with the virus so far claiming three lives. There had previously been only 62 cases in the city.

The virus has now spread across the country to Beijing and Shenzhen and yesterday, South Korea recorded a case. This makes it the third country to diagnose the virus, after cases in Thailand and Japan last week.

But the true scale may be higher?

China, known for its secrecy, say the official cases sit at around 200, but it is believed the true figure is closer to 2000. The MRC Centre for Global Infectious Disease Analysis at Imperial College London said the current figure is more likely to be around 1,723.

A British man has been infected?

Tourist, Ash Shorely, 32, of Lancashire, is feared to be the first western victim, and is currently being treated in hospital in Phuket for a pneumonia-style infection.

Human to human?

The Imperial College research states that “past experience” with SARS and other CoV outbreaks of similar scale “suggests currently self-sustaining human-to-human transmission should not be ruled out.”

Chinese New Year?

The weekend spike has raised concerns that the virus could be spread further by the hundreds of millions of people travelling for Chinese New Year later this month.

What now?

Ongoing monitoring. Meanwhile, the United States and most Asian countries have upped screenings of travellers from Wuhan and the WHO has warned hospitals worldwide of the potential for a wider outbreak.

MAUREEN SUGDEN