LONDON — While Toronto battles the World Health Organization over its classification as a no-go area because of SARS, British experts are backing the United Nations agency for acting to stop the spread of the virus.

Dr. Mahmoud Halablab of King's College in London said the WHO properly responded after it believed the disease was exported from Canada.

"Obviously there are fears there that it may spreading into other countries," he said in an interview on Thursday. "It is a serious bug, it is a new ... a novel virus."

Halablab said the WHO is being cautious because not a lot is known about the virus that causes severe acute respiratory syndrome.

"To understand the behaviour of such a new virus will take a long time," said Halablab, a microbiologist who is an expert on legionnaires' disease.

"And therefore, precautionary measures are really essential at this stage to contain the epidemic or to contain the infection, especially with a mysterious virus."

Dr. Richard Dawood, a travel medicine expert at the Fleet Street Travel Clinic in central London, said the rest of the world should note the British experience in dealing with health emergencies such as BSE, or bovine spongiform encephalopathy.

In the early stages of the so-called mad cow outbreak, government officials waited too long to take the drastic measures needed to contain the disease because it feared an economic crisis.

"Every time we've tried to limit the immediate economic impact of these problems by playing down the dangers, we've been proved wrong," he said.

"With BSE in this country, we had agriculture ministers feeding hamburgers to children to try and calm the public and show that the risk wasn't very real, at a time when faster and more painful action would have brought wider benefit."

In the end, Dawood said, the economic pain was made worse by delaying the proper health response to BSE, and the same was true two years ago when the government responded too slowly to the spread of foot-and-mouth disease in farm animals.

Dawood said he understands the anger that officials in Toronto must be feeling over the WHO travel warning, but trying to curb the number of people travelling through an infected area is worth trying, even though it may be too late.

"Is there a big risk to people from going to Toronto? I don't think so," he said.

"I would say anybody who absolutely has to go, they should certainly go. We're talking about a huge city and a small number of cases. But I think the global community needs to do more to try and contain the problem and we've got very primitive, blunt tools for doing that."

Halablab said the other problem with SARS is there is no effective treatment for it.

"It seems to be a fairly virulent strain. In other words, it's a nasty form of virus," he explained. "Yes the mortality rate is small, less than five per cent overall, but in 40 per cent of the cases it causes severe infection, so that's quite significant."

And the WHO has a responsibility, Halablab added, to protect global health, which means it must take into consideration the impact around the world of people travelling longer distances at a faster pace.

Canada is a developed country with well established medical care, "and yet this epidemic is getting its grip," he said.

"If we imagine the same scenario happening in another country whereby the economic situation is not as good as it is in Canada, like a Third World country or in places where the income per capita is very low and there are no effective measures for controlling infectious diseases, then it would be disastrous."