ficials are closely monitoring a new respiratory virus related to SARS that is believed to have killed at least one person in Saudi Arabia and left a Qatari citizen in critical condition in London.

The germ is a coronavirus, from a family of viruses that cause the common cold as well as SARS, the severe acute respiratory syndrome that killed some 800 people, mostly in Asia, in a 2003 epidemic.

In the latest case, British officials alerted the World Health Organization on Saturday of the new virus in a man who transferred from Qatar to be treated in London.

WHO said virus samples from the patient are almost identical to those of a 60-year-old Saudi national who died earlier this year. The agency isn’t currently recommending travel restrictions and said the source of infection remains unknown.

Health officials don’t know yet whether the virus could spread as rapidly as SARS did or if it might kill as many people. SARS, which first jumped to humans from civet cats in China, hit more than 30 countries worldwide after spreading from Hong Kong.

“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.”

He added it was unclear how the virus spreads. Coronaviruses are typically spread in the air but Hartl said scientists were considering the possibility that the patients were infected directly by animals. He said there was no evidence yet of any human-to-human transmission.

“All possible avenues of infection are being explored right now,” he said.

No other countries have so far reported any similar cases to WHO, he said, and so far there is no connection between the cases except for a history of travel in Saudi Arabia.

Hartl said the first patient may have had an underlying condition but it probably didn’t make him more susceptible to catching the virus.

Other experts said it was unclear how dangerous the virus is.

“We don’t know if this is going to turn into another SARS or if it will disappear into nothing,” said Michael Osterholm, a flu expert at the University of Minnesota. He said it was crucial to determine the ratio of severe to mild cases.

Britain’s Health Protection Agency and WHO said in statements that the 49-year-old Qatari national became ill on Sept. 3, having previously traveled to Saudi Arabia. He was transferred from Qatar to Britain on Sept. 11 and is being treated in an intensive care unit at a London hospital for problems including kidney failure. Respiratory viruses aren’t usually known to cause serious kidney problems.

David Heymann, chairman of the Health Protection Agency, said the new virus didn’t appear that similar to SARS.

Heymann said it was unknown whether the virus might mutate to spread more easily in a dangerous form, since viruses mutate constantly as they reproduce. He said none of the health workers involved in treating the Qatari patient had fallen ill.

The Hajj has previously sparked outbreaks of diseases including the flu, meningitis and polio.

• MARIA CHENG Associated Press