GENEVA — The World Health Organization effectively declared the end to the global spread of severe acute respiratory syndrome Wednesday, while noting it needs to continue surveillance for at least a year.

“The global outbreak, at least in this initial phase, is clearly coming under control,” the WHO said, noting that the number of new cases “has gradually dwindled to the present daily handful” during June.

The WHO, which made the announcement on the 99th day since it first warned of the threat from the SARS virus, said it “is confident that all countries that have experienced outbreaks are disclosing cases fully and promptly — SARS is too big a disease to hide for long.”

But it said the need for “continued vigilance is now greater than ever” and “sees a need for at least a full year of surveillance to determine whether the disease has established endemicity and to ensure that no cases have spread, undetected, to countries with poor surveillance and reporting systems.”

The WHO cited “many unanswered scientific questions, particularly concerning the origins of the virus and the contribution of environmental contamination to overall transmission.”

“Scientists cannot rule out the possibility that the SARS virus hides somewhere in nature . . . only to return when conditions are once again ripe for the efficient spread of infection to its new human host,” it said.

While vaccines, effective treatment and other sophisticated control tools are still unavailable, SARS “has been brought close to defeat by the diligent and unrelenting application — on a monumental scale — of centuries-old control measures: isolation, contact tracing and followup, quarantine, and travel restrictions,” the WHO said.

As of Wednesday, the global SARS death toll stood at 801, with the cumulative number of reported probable cases at 8,465.

Vietnam broke the chain of transmission April 28 as did the Philippines on May 20 and Singapore on May 31. As for China, where SARS is believed to have originated, the WHO has removed most of the affected areas from its lists of travel advisory and SARS hot spots.

As of Wednesday, the WHO designates four areas — Beijing, Hong Kong, Taiwan and Toronto — as hot spots where local transmissions are reported.

Recommendations to postpone all but essential travel have been remove for all areas except Beijing.

However, worried about complacency as the SARS crisis eases, the WHO chief is warning that another epidemic could easily occur and that it is only a matter of time before a new killer disease emerges.

“There will be new threats of this kind, there will be new diseases coming,” Gro Harlem Brundtland, WHO’s director general, said at the close Wednesday of a conference of some 1,000 scientists and health officials to assess the world’s reaction to SARS.

Brundtland said the danger now was that countries may start to think the battle is won. “As long as the virus is there, and as long as patients are carrying it, it can be spread,” she said.

The virus that causes SARS has been found in civet cats and other game animals sold at food markets in southern China, where the epidemic started, raising the possibility the human strain came from animals.

Dr. Hume Field, an Australian veterinary expert, said that if animals are confirmed to be the source of the SARS virus in humans, “eradication is highly improbable.” The potential reservoir that animals could provide for the virus is vast.

He said research indicated the virus had existed in animals for a long time, and recent behavioral changes could have triggered a jump to humans.

“This seems to be an ancient virus,” Field told a panel discussion. “So I don’t think eradication or . . . control of the host animal is the issue. The issue is to avoid exposure.”

Dr. David Heymann, WHO’s communicable diseases chief, said the only way to completely eradicate a virus such as SARS would be to remove it from its host animal population.

Heymann said stopping the human-to-human transmission was just the first step. Still to be found were the origins of the disease, and ways to control how it transfers to people.

Dr. Nigel Gay, a WHO consultant on SARS infection patterns, said it appeared possible the current strain of the virus could be eliminated, though gaps in research left open the possibility of chronic or asymptomatic infections.

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