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Faced with the return of SARS (search), China on Monday ordered wild animals slaughtered by the thousands in the disease's suspected region of origin, a striking response that elicited calls for caution from international doctors concerned about safety and destroying medical evidence.

The decision to kill up to 10,000 civet cats (search) and related specialty-food creatures in the wildlife markets of the southern province of Guangdong -- animals suspected of being SARS carriers -- came as the first case of SARS in China this season was confirmed after more than two weeks of intricate tests.

On Tuesday, Chinese state media said that more than 200 civet cats had already been drowned and the government wants the culling completed by Saturday. The animals are reportedly being killed by lowering them in cages into vats of water.

Adding to Asia's SARS unease, a husband and wife in the Philippines who fell ill after returning from Hong Kong were placed in isolation to await test results. And Hong Kong stepped up health surveillance at border checkpoints with mainland China.

The World Health Organization (search), upgrading the case of an ailing 32-year-old Guangdong television producer from suspected severe acute respiratory syndrome to a definite diagnosis, urged calm. It said China, which became a travel pariah during the first outbreak last year, was safe.

"We have to be very clear about it: It does not mean that one case can lead to a public health threat," said Dr. Henk Bekedam, the WHO representative for China. But the national government warned its citizens: "Be vigilant."

China's leadership, criticized for a sluggish response to the debut of SARS last year, lurched in the other direction with an extraordinary, aggressive decision: to eradicate civets from Guangdong's wildlife markets, where they are sold as delicacies and are a strong part of the local economy.

"We will take resolute measures to close all the wildlife markets in Guangdong and to kill the civet cats," said Feng Liuxiang, vice director of the Guangdong Health Department.

Zhong Nanshan, director of the Guangzhou Institute of Respiratory Diseases, said species related to civets also will be killed, including raccoon dogs, ferret badgers, hog badgers and Eurasian badgers.

The slaughter will be completed by Saturday, the government said. It wasn't clear when the cull would begin, or who would carry it out and under what circumstances.

Guangdong's wildlife markets were ordered closed Monday, and the provincial Forestry Department put 2,030 presumably doomed civet cats in quarantine. The official Xinhua News Agency called the civet a "major SARS virus carrier."

WHO is less definitive about civet-SARS links. One of its animal experts, Dr. Jeffrey Gilbert, emphasized that while the weasel-like mammals have been "implicated" in the disease's possible transfer from animals to humans, definitive proof is elusive.

He said the "radical step" of mass slaughter must be conducted under controlled conditions to avoid contamination of places or people that could spread SARS. What's more, he said, any reckless cull could eliminate clues to the illness' "animal reservoir."

"We would recommend that the authorities do undertake extreme caution. There is a potential hazard there," Gilbert said at a news conference. WHO had expressed unease in August when China, after outlawing the trade of civets for four months, rescinded the ban.

The disease eventually christened SARS, which first broke out in Guangdong in November 2002, infected more than 8,000 people and killed 774 worldwide -- mostly in Asia -- before it was brought under control in June. In China, 349 died.

China's newest SARS patient tested positive in one sample of many, WHO said. But SARS team leader Dr. Julie Hall, in Beijing, said examinations of that sample convinced doctors that the man was infected.

The confirmation represented the first known case of SARS contracted in China since July -- and the first this season to come from the general population. Two other cases -- in Singapore and Taiwan -- were linked to researchers apparently exposed in labs.

Meanwhile, Singapore has increased its use of thermal scanners to screen travelers from Guangzhou at Changi Airport's arrival halls, said Albert Tjoeng, a spokesman for the Civil Aviation Authority of Singapore. The scanners read the temperature of travelers and can help determine who has SARS.

The patient's condition was stable Monday, and those who came into contact with him have shown no symptoms. Both WHO and the government said they didn't yet know how the man contracted the virus, though he reported neither eating nor coming into contact with wild game.

Researchers at Hong Kong University said they found similarities between a virus found in civets and in the suspected SARS patient, suggesting the disease might have recently jumped from animals. Those findings, not independently verified, apparently prompted the plans for the civet eradication.

The quick announcement of the confirmed case -- the government reported it before WHO could -- was a sharp departure from China's initial responses to the virus last year. International observers complained of stonewalling, bad information and a reluctance to acknowledge the problem.

In late April, China fired its health minister and promised a more open and aggressive approach, something even many of its critics abroad say it has moved toward. At home, citizens didn't seem especially alarmed, even after learning of the new case Monday.

"The government has reacted quickly because it learned about SARS from the last time," newsstand worker Zhou Bao said as he unbundled stacks of magazines.

"Don't worry," added Beijing fruit-stall vendor Xiu Yuling. "And even if you catch it, being worried won't help."