Global health officials are closely monitoring a new respiratory virus related to Severe Acute Respiratory Syndrome (SARS) that has left a Qatari citizen in critical condition in a hospital in London.
The UN's World Health Organisation (WHO) put out a global alert on Sunday saying a new virus had infected the 49-year-old man who had recently travelled to Saudi Arabia - where another man was killed by an almost identical virus.
Britain's Health Protection Agency (HPA) and respiratory disease experts said there was no immediate cause for concern, although authorities were watching out for any signs of the virus spreading.
The virus, known as a coronavirus, comes from the same family as both the common cold and SARS, the syndrome that killed 800 people in a 2003 epidemic.
The WHO said it was not recommending any travel restrictions at the moment but would seek further information on the virus.
Health officials said they did not know yet whether the virus could spread as rapidly as SARS did, or if it would be as lethal.
"It's still [in the] very early days," said Gregory Hartl, a WHO spokesman. "At the moment, we have two sporadic cases and there are still a lot of holes to be filled in."
Coronaviruses are typically spread in the air, but Hartl said scientists were considering the option that the patients were infected directly by animals as there was no evidence yet of any human-to-human transmission.
No other countries have so far reported any similar cases to WHO, he said, and so far there is no connection between the two cases except for a history of travel in Saudi Arabia.
Andrew Easton, a virologist at Britain's University of Warwick, told the Reuters news agency that with only two cases so far, it was difficult for experts to estimate the potential threat.
"The important thing is to be aware of the virus and to be on the lookout for any evidence that it is more than a rare chance event," he said.
Hugh Pennington, a professor of bacteriology at the University of Aberdeen, told Al Jazeera that medicine had also advanced since the SARS outbreak, and that technology would allow faster diagnosis.
"The lessons we’ve learned from SARS have been extremely useful," he said. "We now have techniques which mean you can do a very rapid fingerprinting of the RNA in somebody’s lungs if they’ve got a very unusual pneumonia.”
The HPA and WHO said in statements that the Qatari national became ill on September 3, after previously having travelled to Saudi Arabia.
He was transferred from Qatar to Britain on September 11 and is undergoing treatment in an intensive care unit at a London hospital for complications, including kidney failure.
The HPA said it had conducted lab testing on the Qatari's case and found a 99.5 per cent match to the virus that killed the 60-year-old Saudi national earlier this year.
David Heymann, chairman of the HPA, said the new virus did not appear that similar to SARS.
"It isn't as lethal as SARS and we don't know too much about its transmissibility yet," he said. "If people are getting infected, they aren't getting serious symptoms."
He added that none of the health workers involved in treating the Qatari patient had fallen ill.
Saudi officials said they were concerned that the upcoming Hajj pilgrimage next month, which brings millions of people to Saudi Arabia from all over the world, could provide more opportunities for the virus to spread.