Even though the SARS virus does not appear to have mutated significantly since it spread from Asia, a leading expert said Sunday it is early in the epidemic and the virus could yet evolve to cause either a more lethal or milder disease.
Some scientists believe that recent genetic comparisons of 14 different samples of the virus indicate SARS may have made the mutations it needs to in order to adapt to humans.
"Yes, for now. 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]," said Dr. Christian Drosten, a virologist at the Bernhard-Nocht Institute for Tropical Medicine in Hamburg, Germany.
"What will happen to the virus when it jumps from Asians into a genetically different population, say sub-Saharan Africans?" he said.
"This is something that people do not think closely about," said Drosten, whose lab belongs to the World Health Organization (WHO) collaboration investigating the virus.
"There is an interaction between the genetics of the host and the genetics of the virus and there could be different interactions if there is a different genetic background in the host. There may be pressure on the virus to change again. This is what we see in many other viruses," he said.
In a study published in The Lancet medical journal last week, researchers compared the genetic makeup of SARS virus samples taken from 14 people to examine how much the bug is mutating.
The SARS virus is a new member of the coronavirus family, a group of viruses that is known to have a high mutation rate.
However, the results indicated that the virus has remained surprisingly consistent as it has passed from person to person.
There had 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, but there is no evidence the mutations have altered the seriousness of the disease.
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.
Drosten, speaking at a conference of the European Society of Clinical Microbiology and Infectious Diseases, noted that the virus samples analyzed so far were culled from people who became sick within only a few weeks of each other.
Experts say the SARS virus will certainly keep mutating, but they don't 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.
SARS has made more than 7,000 people ill around the world and killed more than 500.
The WHO estimates that about 15 percent of people who come down with 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, the WHO estimates.
The outbreak, which began in November, is waning in many parts of the world, the organization says. Vietnam is now SARS-free and health officials hope that Hong Kong, Singapore and Toronto will soon follow.
"The outbreak, we feel, is over in Toronto," Dr. Donald Low, chief microbiologist at the city's Mount Sinai Hospital, told the conference.