ลองมองย้อนไปดูโรคปริศนาในอดีตมนุษยชาติ(english)

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spread of a mysterious respiratory illness to a number of Asian countries and Canada has led the World Health Organization to declare it "a worldwide health threat" — but little is known about the ailment.

The health organization calls the illness severe acute respiratory syndrome, or SARS. No one knows why it suddenly appeared or what causes it. So far, laboratory tests have told doctors only what it is not. And with the illness failing to respond to antibiotic and antiviral drugs, standard supportive nursing care and infection control measures seem the only treatment available.

No one can even say for sure how many people have come down with the disease. Health officials estimate SARS has caused at least 9 deaths among nearly 500 cases.

The uncertainty has fed unease.

Years of warnings about newly emerging diseases, not to mention bioterrorism, have left Americans jittery about rare and mysterious diseases.

Health officials have long predicted that influenza would strike again as it did during World War I in 1918 and 1919, causing 20 million deaths worldwide. SARS has revived those concerns just as the United States is on the verge of war with Iraq.

Its emergence now — especially because it seems to be striking young adults — is an eerie reminder of how diseases can affect military operations.

Health officials must confront two crucial questions: Is SARS an unknown form of a known disease like influenza? Or is it caused by a novel infectious agent? If past outbreaks of new diseases are a guide, the answers may take time in coming.

Tick-borne Lyme disease was regarded as a new disease when it was given that name in 1977. It took four years after its detection in Connecticut to identify the causative agent, a spirochete bacterium, Borrelia burgdorferi, a microbe that had been identified for decades. For example, the same disease occurred as early as 1909 in Sweden.

After Legionnaire's disease struck in Philadelphia in 1976, it took six months before discovery of the causative bacterium, Legionella pneumophila. Meanwhile, researchers pursued many blind avenues, including toxins.

It took months to identify the Ebola virus from outbreaks in Africa.

When the disease now known as AIDS was first identified in 1981, scientists debated whether it was caused by an infectious agent or a toxin. It took about two years to discover what is now known as H.I.V. And two additional years passed, to 1985, for general scientific acceptance that H.I.V. caused AIDS.

But in trying to solve the riddle of SARS, health officials have some advantages over the scientists who confronted these outbreaks. Laboratory techniques have become more sophisticated in recent years. The government has invested money to strengthen the public health system to improve the tracking of new and emerging infections. And since the Sept. 11 attacks the government has invested additional money to improve the ability of state and local health departments to detect and prevent bioterrorism.

The researchers trying to unravel the SARS mystery will benefit from these public investments, but they still face a number of obstacles.

A logical first assumption was the possibility that the influenza virus — either a strain that had rarely infected people or one created by a major new mutation — caused SARS. Health officials say the only thing predictable about influenza is its unpredictability. New strains emerge regularly, and they vary widely in virulence.

Still, when health officials heard of the symptoms associated with SARS — fever, aches, difficulty breathing — they focused on avian flu, or flu spread from birds to people. In particular, they wondered about a rare strain known as A(H5N1).

The World Health Organization told health officials to look out for suspicious cases after the avian strain killed one person and sickened another in Hong Kong last month. And the same strain had infected 18 people in Hong Kong in 1997, killing 6.

In New Outbreak, Eerie Reminders of Other Epidemics
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The strain is lethal to chickens, but not to other birds like ducks. In 1997, Hong Kong officials ordered the slaughter of all of its 1.4 million chickens out of concern that the strain might cause an epidemic there and elsewhere.

But in recent weeks scientists at laboratories in at least five countries have failed to detect the avian flu strain in any SARS case. Dr. David L. Heymann, executive director in charge of communicable diseases for the W.H.O., said, "We have not ruled out influenza definitively." But many experts are wondering whether they are confronting a previously unknown infectious agent, possibly one of animals that has jumped species to humans.