PARIS, May 8: The most complete genetic study to date of the SARS virus has revealed an agent that appears to undergo almost negligible mutation, a phenomenon that is described as “a double-edged sword” for the doctors battling to eradicate it.

Scientists in Singapore compared the genetic ID of samples of Severe Acute Respiratory Syndrome (SARS) virus, taken in throat swabs from local patients, with the genome of samples found in other countries.

The most important areas of the genomes were identical, something that is remarkable in so-called RNA viruses, which includes SARS and other members of the coronavirus family.

Usually, RNA viruses mutate very quickly, changing a letter or so in their genetic code every time they replicate. This evolution is part of the virus’ drive to survive, perhaps finding ways of evading the defence mechanisms of its host or of transferring to a new and more profitable host.

The research, published online late Thursday by the British medical weekly The Lancet, was carried out by a team led by Edison Liu from Singapore’s Genome Institute.

They sequenced the genetic code of a SARS virus taken from one of the first known carriers of the disease, and of SARS viruses found in four people in Singapore who had had direct or secondary contact with that individual.

These sequences were compared with virus isolates from Canada, Hanoi and Hong Kong and from Guangzhou and Beijing in China.

The 14 sequences contained small signatures that pointed to where they originated - something that could be a useful epidemiological tool — but there was no major variant in their genetic machinery.

In a commentary also published by The Lancet, molecular biologists Earl Brown and Jason Tetro from the University of Ottawa, Canada, said that Liu’s evidence pointed to “a remarkable genetic conservation” of the virus since the outbreak was first documented in February.

“This finding may be a double-edged sword,” they warned.

It shows that the virus is well adapted to lodging in the human host — in other words, there is the risk that it is here to stay.—AFP