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SARS: A learning experience, a lurking fear

Though perplexing SARS has ducked out of sight, it is still on scientists' minds. The specter of re-emergence dampens health lessons learned.

By LISA GREENE
Published January 31, 2005

The mysterious fever bolted out of south China and spread illness and death across the globe. As the cases mounted into the thousands, its name - SARS - became a new word for fear.

And then, just a few months later, it disappeared.

Scientists warned then, in mid 2003, that SARS would return. This new disease is here to stay, they said. It would come again, probably that very winter.

But it didn't.

And so far, almost two years after the disease first appeared, it hasn't re-emerged.

Why not?

The short answer: Scientists don't know.

"We're very gratified that it hasn't come back," said Dr. William Schaffner, chair of preventive medicine at Vanderbilt University and a board member of the National Foundation for Infectious Diseases. "We may be perplexed, but we are not complaining."

Scientists have theories about SARS, or severe acute respiratory syndrome. They include everything from how animals are slaughtered in Guangdong, China, to how the virus is transmitted, but there are no definite answers.

But on one thing, scientists agree: It's too soon to say SARS is gone for good.

* * *

As a top epidemiologist at the federal Centers for Disease Control and Prevention, Dr. Umesh Parashar has traveled the world investigating disease outbreaks. He went to Malaysia in 1999, where a new virus, nipah, was so deadly that it killed 40 percent of the people who caught it. But when Parashar arrived in Hong Kong in 2003, this outbreak seemed different. "It was so strange," he said. "I've never felt personally vulnerable the way I did with the SARS virus."

The first time Parashar walked into a meeting at a Hong Kong hospital, he immediately realized he looked out of place: "I was the only person in the room without a mask."

That changed quickly. Everyone was afraid, Parashar said, because so little was known about the new disease - except that it seemed to spread quickly and easily. Investigators asked SARS patients to fill out forms to learn more about how the infection spread. Some clerks refused even to touch the forms, fearing they might be teeming with germs.

Since that trip, Parashar has become lead medical epidemiologist of the CDC's SARS task force. But he has no idea when, or whether, SARS will return. "The possibility for a resurgence remains," he said. "It's something we have to watch for. I don't think anybody can put a time frame on when we'll be out of the woods."

Other new viruses have appeared, then vanished for a long period before returning in deadly fashion, Parashar pointed out.

The ebola virus, which kills up to 90 percent of its victims, was first identified during 1976 outbreaks in Sudan and Zaire that killed more than 400 people. A small 1979 outbreak killed 22 in Sudan, but only a handful of cases were reported until 1995, when 315 people in the Democratic Republic of the Congo fell ill. Ebola killed 250 of them.

Nipah virus killed 105 people when it first emerged in Malaysia in 1999. It, too, was quiet - until last spring, when it infected at least 53 people in Bangladesh, killing 35.

Diseases wax and wane for reasons scientists still don't understand, Schaffner said. He pointed to influenza, which changes each year from one strain to another, some more deadly, some less so, with little pattern or predictability. "Influenza is fickle," he said.

Such diseases are hard to kill because they have a natural home in animals. The nipah virus lives in some types of fruit bats. People have become infected with ebola after handling infected chimpanzees, monkeys, gorillas and forest antelopes.

Scientists speculate that changes in how animals are handled there may have helped stop SARS.

"It might be a change in the way (animal) markets function," said Dr. John Sinnott, director of the Florida Infectious Disease Institute at the University of South Florida. He visited Thailand, where nine people contracted SARS, last summer and saw "significant changes" in the animal markets since his last visit two years earlier - before SARS. Those included lining cages with foam, so animals are less likely to pass infection to others.

Dr. Frederick Southwick, chief of infectious diseases at the University of Florida, also pointed to Guangdong. "We think it started with people slaughtering live animals that had the virus," he said. "I think they have changed some of their practices."

However, if civet cats aren't the natural host for the disease, it may be that few of the trapped animals are infected with SARS. "They just happened to trap the wrong civet and bring it in for the disease to occur," Sinnott said.

Or it could be that something else has to happen for SARS to spread among people.

"There is evidence that the virus evolved after it jumped to humans," Parashar said. "That may have affected its ability for transmission among humans."

Dr. Stanley Perlman, a pediatrics and microbiology professor at the University of Iowa, is one of a handful of U.S. researchers who have studied coronaviruses, the family that SARS comes from, for decades. Perlman thinks a SARS outbreak may take just the right mix of circumstances.

"In 2003, it had to adapt to the human population," Perlman said. "In the epidemic, it crossed (from animals to humans) 11 times, but only one time did it really spread. The virus isn't naturally virulent."

It's even possible, Perlman said, that SARS has returned, but remained so mild that those infected mistook it for the common cold.

Scientists also wonder whether people in Guangdong now have immunity to SARS, so that they won't become sick again. That's possible, but some small studies, where people's blood was drawn to look for antibodies, showed few people with immunity, Schaffner said. "That also suggests SARS was something new in the population," he said. "We don't know why. Those animal markets have been there for the last millennium. ... Why did it suddenly occur?"

Even though they don't know when, or if, it will happen, doctors say they're better prepared now for SARS to come back. Doctors have a better idea of what works well, including quick isolation of sick patients and strict enforcement of hospital policies to control infection. They also know that some costly, cumbersome measures, including broad quarantine of people exposed but not ill, and taking temperatures of air travelers, seemed to have little effect.

The World Health Organization gained more political importance and more power to act aggressively during the next pandemic, Southwick said.

Schaffner hopes health officials have learned from China's early efforts to keep SARS secret. "It told everybody who hadn't gotten the word that keeping things to yourself cannot work in the modern world," he said.

Scientists say they have to be ready for other diseases as well. SARS is just a sign, they said, of how fast a new disease can explode across a world in which germs travel at the speed of a 747.

"SARS will not be the last emerging infection," Sinnott said. "It was a warning shot across the bow."

[Last modified January 31, 2005, 00:38:15]