* Five of 12 patients with new coronavirus have died
* Study finds virus "grows very efficiently" in humans
* Could be treated with interferon drug immunotherapy
* Swift research needed to find where virus came from
By Kate Kelland, Health and Science Correspondent
LONDON, Feb 19 (Reuters) - A new virus that emerged in the Middle East last year and has killed five people is well adapted to infecting humans but could potentially be treated with drugs that boost the immune system, scientists said on Tuesday.
The virus, called novel coronavirus or NCoV, is from the same family as the common cold and as SARS, or Severe Acute Respiratory Syndrome. There have been 12 confirmed cases worldwide - including in Saudi Arabia, Jordan and Britain - and five patients have died.
In one of the first published studies about NCoV, which was unknown in humans until it was identified in September 2012, researchers said it could penetrate the lining of passageways in the lungs and evade the immune system as easily as a cold virus can.
This shows it "grows very efficiently" in human cells and suggests it is well-equipped for infecting humans, said Volker Thiel of the Institute of Immunobiology at Kantonal Hospital in Switzerland, who led the study.
NCoV was identified when the World Health Organisation issued an international alert in September saying a completely new virus had infected a Qatari man in Britain who had recently been in Saudi Arabia.
Coronaviruses are a family of viruses that includes those that cause the common cold as well as the one that caused SARS - which emerged in China in 2002 and killed about a 10th of the 8,000 people it infected worldwide.
Symptoms of both NCoV and SARS include severe respiratory illness, fever, coughing and breathing difficulties. Of the 12 cases confirmed so far, four were in Britain, one was a Qatari patient in Germany, two were in Jordan and five in Saudi Arabia.
Scientists are not sure where the virus comes from, but say one possibility is it came from animals. Experts at Britain's Health Protection Agency say preliminary scientific analysis suggests its closest relatives are bat coronaviruses.
What is also unclear is what the true prevalence of the virus is - since it is possible that the 12 cases seen so far are the most severe, and there may be more people who have contracted the virus with milder symptoms so are not picked up.
"We don't know whether the cases (so far) are the tip of the iceberg, or whether many more people are infected without showing severe symptoms," said Thiel, who worked with a team of scientists from the Netherlands, Switzerland, Germany and Denmark. "We don't have enough cases to have a full picture of the variety of symptoms."
Thiel said that although the virus may have jumped from animals to humans very recently, his research showed it was just as well adapted to infecting the human respiratory tract as other coronaviruses like SARS and the common cold viruses.
The study, published in mBio, an online journal of the American Society for Microbiology, also found that NCoV was susceptible to treatment with interferons, medicines that boost the immune system and which are also successfully used to treat other viral diseases like Hepatitis C.
This opens up a possible mode of treatment in the event of a large-scale outbreak, the scientists said.
Thiel said that with the future of the virus uncertain, it was vital for laboratories and specialists around the world to cooperate swiftly to find out more about where it came from, how widespread it was, and how infectious it might be.
"So far it looks like the virus is well contained, so in that sense I don't see any reason for increased fear," he said. (Editing by Pravin Char)