(Reuters) - A Qatari man struck down with a previously unknown virus related to the deadly SARS infection and the common cold is critically ill in hospital in Britain, the World Health Organisation said on Monday.

be struck down:击倒

The U.N. health body 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 with an almost identical virus had already died.

put out a global alert:发布一项全球警报

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.

Health Protection Agency:健康保护局

respiratory disease experts:呼吸道疾病专家

watch out for:小心提防

"This new virus ... is different from any that have previously been identified in humans," the HPA said.

Any suggestions of a link between the virus and Saudi Arabia will cause particular concern in the build-up to next month's Muslim haj pilgrimage, when millions of people arrive in the kingdom from across the world, then return to their homes.

The virus, known as a coronavirus, comes from the same family as SARS which emerged in 2002 and killed 800 people.

SARS:Severe Acute Respiratory Syndromes 非典型性肺炎

"This is now an international issue," WHO spokesman Gregory Hartl said. "The (Qatari) patient is still alive but, as we understand, in critical condition," he said.

WHO:World Health Organization 世界卫生组织

The HPA said it was recommending the Qatari patient be treated in isolation by doctors and nurses wearing gowns, gloves respirators, goggles and other protective equipment.

It did not recommend any specific actions for travelers or other members of the public.