The SARS (search) virus does not appear to have mutated significantly in the eight weeks since it spread from Asia, but a leading expert said Sunday the virus still could evolve into a more dangerous form if it enters a race of people with a different genetic background, such as sub-Saharan Africans.

So far, most of the world's 7,200 SARS cases and 536 deaths have been in Asia, with the vast majority in China and its territory of Hong Kong. The biggest outbreak outside Asia has been Canada's Toronto area, with 22 deaths, though the World Health Organization (search) says the disease has been contained there.

"There may be pressure on the virus to change again. This is what we see in many other viruses," said Dr. Christian Drosten, a virologist at the Bernhard-Nocht Institute for Tropical Medicine (search) in Hamburg, Germany.

He was speaking at a conference of the European Society of Clinical Microbiology and Infectious Diseases in Glasgow.

In a study published in The Lancet medical journal earlier this week, researchers compared the genetic makeup of SARS virus samples taken from 14 people to examine how much the bug is mutating.

The results indicated that the virus has remained surprisingly consistent as it has passed from person to person — even though the SARS virus is a new member of the coronavirus family, a group of viruses known to have a high mutation rate.

Some scientists believe the genetic comparisons of the 14 different samples indicate that the SARS virus mutations have run their course.

But Drosten noted that the virus samples analyzed so far were culled from people who became sick within only a few weeks of each other.

"But it has only been a few weeks. It took decades to get more virulent strains of HIV, and that is a retrovirus, which should mutate more than (SARS)," Drosten said. "What will happen to the virus when it jumps from Asians into a genetically different population, say sub-Saharan Africans?"

There have been a handful of mutations, which led to the virus splitting into two geographically distinct strains that provide signatures to help scientists trace the origin of an individual's infection. There is no evidence the mutations have altered the seriousness of the disease.

Drosten's lab belongs to the WHO collaboration investigating the virus.

The consistency of the virus is considered a double-edged sword. While it has not mutated into a more deadly form, it has not mellowed into a weaker germ.

Experts say the SARS virus certainly will keep mutating, but they do not know whether those mutations will change the seriousness of the disease. So far, WHO scientists say there is no evidence that this is happening — the disease looks the same around the world.

The WHO estimates that about 15 percent of people who contract the disease die, suggesting the illness is more deadly than influenza or other common respiratory infections. For people over 65, the death rate is about 50 percent, WHO estimates.

The outbreak, which began in November, is waning in some parts of the world, though it still is spreading quickly in China and Taiwan. Vietnam is now SARS-free and health officials hope Hong Kong, Singapore and Toronto will soon follow.

On April 30, the WHO lifted an advisory warning people against unnecessary travel to Toronto.