The mystery virus which has claimed the lives of more than 150 people worldwide is a new form of the common cold, scientists have confirmed.
Sars has infected thousands of people
The World Health Organization said tests prove severe acute respiratory syndrome (Sars) is a mutant form of the corona virus, the cause of the common cold.
Officials at WHO hailed the discovery, saying it will allow scientists to concentrate on developing treatments and a potential cure for the deadly disease.
Sars has affected over 3,000 people in more than 20 countries around the world.
These latest tests were carried out by scientists at Erasmus University in Rotterdam, Netherlands.
They are one of 13 laboratories from 10 countries working with the WHO to combat the virus.
The scientists infected monkeys with the strain of the corona virus suspected of causing Sars.
They found that the animals developed the same symptoms of the disease as humans. The test was a crucial step in verifying the cause of the disease.
We now know with certainty what causes Sars
Although experts have thought that a new strain of the corona virus was the main cause of Sars, it has remained unclear whether
infection with a second type of virus, the human metapneumovirus, makes the illness worse.
Their tests were made possible by studies published last week, which suggested Sars was a new virus.
Scientists from eight countries, including Germany and the United States, found it was not consistent with any other known virus.
They also carried out genetic tests on the virus, which found it was "only distantly related" to known corona viruses.
Dr David Heymann, executive director of WHO communicable diseases programmes, hailed scientists' efforts to identify the virus.
"The pace of Sars research has been astounding," he said. "Because of an extraordinary collaboration among laboratories from countries around the world, we now know with certainty what causes Sars."
Dr Heymann said the discovery would now enable scientists to concentrate on developing diagnoses kits and treatments.
"Now we can move away from methods like isolation and quarantines and move aggressively towards modern intervention strategies including specific treatments and eventually vaccination.
"With the establishment of the causative agent, we are a crucial step closer," he said.
'New to science'
The discovery will also help scientists trace the evolution of Sars and could help them determine whether it jumped from animals to humans.
Tests are ongoing in pigs and poultry to see how susceptible those animals are to Sars.
Researchers at the University of Hong Kong said a new
genetic sequencing of the Sars virus proves conclusively
that it came from animals.
Malik Peiris, a microbiologist at the university, described Sars as "something that is new to
He also dismissed claims that it could have been spread by terrorists.
"That whole genome is essentially new," he said. "Nature has been the terrorist throwing up this virus."
On Tuesday, a German biotechnology company said it was distributing a new high-speed test for Sars.
Their test identifies this strain of the corona virus which has now been confirmed as causing Sars.
The firm Artus is confident the test can confirm the presence of the lethal respiratory disease in two hours, whereas traditional tests for antibodies take more than 10 days.