Scientists in Hong Kong have claimed a key breakthrough against a virulent form of pneumonia which is claiming more victims around the world.
Patients are being treated in at least three continents
The researchers have identified the mystery respiratory illness at the heart of a global health scare as a virus from the paramyxoviridae family, which are responsible for conditions such as mumps and measles.
More work is needed to establish whether the virus is a new strain and whether it is curable, according to the doctors from the Chinese University of Hong Kong and Prince of Wales Hospital.
But a university spokeswoman told BBC News Online that the discovery indicated that the treatment being given to patients suffering from the atypical pneumonia in Hong Kong - the hardest-hit area - was the right kind.
Scientists at the hospital analysed a speciman taken from a hospital worker who had contracted the illness. Evidence of the same virus was also found in two other hospital workers who developed similar symptoms.
John Oxford, professor of Virology at Queen Mary's School of Medicine, said a similar virus had been discovered in Holland last year.
"It is rather slow-moving, rather restricted to families and hospitals, not a rip-roaring affair, but still very nasty.
"There are no anti-viral drugs against this family of viruses, and there are no vaccines available. It will be a question of several years work.
"But it is not fantastically infectious, so I wouldn't expect there to be a massive outbreak in other parts of the world."
The World Health Organization (WHO) has described the illness as a "worldwide health threat" and issued a rare emergency warning after cases were reported on three continents, with more suspected in other parts of the world.
Death toll fears
The latest possible victim of the illness - dubbed Severe Acute Respiratory Syndrome (Sars) - was a doctor in Vietnam who died on Wednesday.
The Frenchman had been involved in the treatment of an American businessman believed to have been suffering from the illness.
A nurse who also cared for the American in Hanoi died earlier.
Authorities in Hong Kong are investigating the death of an elderly man apparently suffering from the atypical pneumonia, the symptoms of which include a high fever, chills, a cough and breathing problems.
Residents of Hong Kong are taking precautions
In total the virus is thought to have killed up to 16 people, and put hundreds more in intensive care.
There are reports of new cases in China, where the disease may have originated, and in Germany, France, Romania and Britain among other countries.
A man in Dublin who has just returned from south east Asia is also thought to be suffering from the disease.
The WHO has now recorded 219 people falling ill with the virus, 123 of them in Hong Kong.
However, the WHO believes prompt action by local health authorities appears to have limited the spread in Europe and North America.
Dr David Heymann, WHO executive director of communicable diseases, said: "The outbreak, we feel, is on its way to containment at least outside of Vietnam and Hong Kong, and China if it is linked."