The World Health Organization has issued an international alert after the discovery of a new respiratory illness similar to the Sars virus which swept the world in 2002.
The disease was identified in a 49-year-old man in Qatar, who is now being treated in a London hospital. Another sufferer from Saudi Arabia has since died.
There have been reports of a small number of other cases of serious serious respiratory illness in the Middle East over the past three months.
The Qatari man was first reported ill on 3 September, and was transferred to the UK a week later. He had previously visited Saudi Arabia.
The UK's Health Protection Agency conducted laboratory tests and has confirmed the presence of a new coronavirus.
Coronaviruses are a large family of viruses which includes those that cause the common cold and SARS. This new virus, however, is different from any previously identified in humans. Symptoms include fever, cough, shortness of breath, and breathing difficulties, and there are as yet no specific recommendations on treatment.
The HPA says that the disese is unlikely to be easily transmitted, as, if it were, more cases would have been expected. The incubation period is believed to be about seven days.
"Given that this is a novel coronavirus, WHO is currently in the process of obtaining further information to determine the public health implications of these two confirmed cases," says the WHO.
It says it's not recommending any travel restrictions, although it is offering advice to Haaj pilgrims, here.
"As we are aware of only two cases worldwide and there is no specific evidence of ongoing transmission, at present there is no specific advice for the public or returning travellers to take but we will share any further advice with the public as soon as more information becomes available," says Professor John Watson, head of the respiratory diseases department at the HPA.