The World Heath Organisation (WHO) has officially confirmed that a member of the corona virus family never before seen in humans causes the flu-like SARS virus which has killed about 160 people worldwide.
Scientists and the WHO have long suspected that the virus, which also causes the common cold, was at the source of SARS, or severe acute respiratory syndrome.
But official identification was a crucial step and will allow them to focus attention on finding specific treatments and possibly a vaccination, WHO officials said.
"With the identification of the corona virus as the causative agent, now we can develop more specific diagnostic tests for this pathogen," Klaus Stohr, coordinator of the UN agency's collaborative network of 13 SARS research laboratories, told a news conference in Geneva.
"Now the research can focus on this virus. The research will help us develop new drugs... Now one can also think about vaccines, if there's a need," he said.
But, Stohr added, experts were optimistic the disease could be controlled using existing measures, helped by a better understanding of its genetic composition which would also improve global surveillance.
Scientists have been in close collaboration since the WHO issued a global alert on the virus, which has been carried by air travel to 23 countries in the past six weeks and infected more than 3,400 people.
During a one-day meeting in Geneva, they will also discuss a strategy for developing a "reliable and dependable" diagnostic test for use in both developed and developing countries.
Current diagnostic tests already exist which can find and amplify bits of genetic material, even in people without typical symptoms of high temperature, a dry cough and breathing difficulties. But they cannot distinguish between live viruses and viruses which do not cause disease.
WHO officials appeared to shrug off fears that a more virulent strain of the disease had developed in Hong Kong, affecting young and healthy people, saying young people had died from the disease in its early stages. While it began in older health workers, it would affect other ages as it spread into other populations, Heymann said.
However Stohr warned that the corona virus family tended to mutate relatively quickly. "It wouldn't be a big surprise if this virus was gradually changing its genetic makeup. How much this change impacts...its capacity to cause disease...remains to be seen," he said.
Heymann said WHO was sending reinforcements and a travel expert to China, epicentre of the virus, and where WHO officials believe the number of cases in the capital Beijing could be underestimated by a factor of five.
"The spring holiday is coming up in May and they're afraid that the disease will spread with internal travel within China," he said. If it set aside sufficient resources, Beijing could cope, but the team feared poorer regions would struggle to control outbreaks, Heymann added.
"Their concern is in the provinces, especially in the western provinces. They are afraid that it will not only spread to cities into the communities but into areas where there may not be health facilities that are closely accessible," he said.