COL SARS might never go away

By Gina Kolata

New York Times News Service

In a remarkable display of international cooperation and technical expertise, scientists already have isolated the virus that causes severe acute respiratory syndrome, or SARS. They know its genetic sequence.

So now, in this amazing age of molecular genetics and medicine, at a time when a new viral disease is entering the human population, can scientists stop it? Can they erase its traces from the human race and set up a vaccine barricade it cannot breach?

The answer, virologists say, is probably not, though prospects for effective drugs and vaccines are good.


The very question, said Dr. John La Montagne, the deputy director of the U.S. National Institute of Allergy and Infectious Diseases, reminded him of a time, two decades ago, when medical experts were flush with their success in eradicating smallpox. The Pan American Health Organization conducted a meeting in a Washington auditorium to ask what disease could be eradicated next.

"All the old warriors were there," La Montagne recalled. But, they agreed, the list of possible diseases was short, for several reasons, among the most important of which was the requirement that the human disease be unique to humans, with no animal host.

"If you have an animal reservoir, unless you eradicate it in the animal, you can't eradicate it," explained Dr. Frederick C. Robbins, a virologist and Nobel laureate who is university professor emeritus at Case Western Reserve University.

That means, La Montagne added, that flu is not a likely candidate for eradication. "There are so many flu viruses in animal species," he said, with viruses infecting birds, pigs, horses -- even ferrets.

Some experts at the meeting 20 years ago suggested polio as a target. Like a few other diseases, measles and syphilis among them, it infects only humans. And there is a vaccine. But, Robbins said, polio still proved a tougher one than smallpox.

Spotting the culprits

One problem is to stop outbreaks when not everyone has been immunized. With smallpox, that can be done. It is clear when people are infected: They break out in horrible pox. This makes it possible to identify and isolate them and to trace their contacts. With polio, Robbins said, most people who are infected never realize it, and so when immunization is incomplete, the disease can spread. Polio patients usually develop mild, temporary gastrointestinal symptoms. Rarely do people suffer the paralysis that makes polio so terrifying.

A World Health Organization campaign began in 1988 with the goal of eradicating polio by 2000. It reduced the number of reported cases from 350,000 in 1988 to 3,500 in 2000, but the disease remains in 20 countries, mostly in South Asia and sub-Saharan Africa.


It also helps to know how many people are immune to the disease. With smallpox, scars mark those who have recovered, and the vaccination leaves a distinctive mark. But the only way to know if someone is immune to polio is to look for antibodies to the virus in their blood.

"Measles is even tougher," Robbins said. "It is highly contagious, and there are other things that cause rashes. And it is not as easy to isolate the virus as it is with smallpox and polio," making diagnosis even more difficult.

Some say public health officials should simply abandon the ideal of eradicating diseases. Dr. D.A. Henderson, a leader in the smallpox vaccination campaign, called disease eradication "a siren song."

So where does that leave SARS?

The good news, said Dr. Kathryn V. Holmes, a leading expert on coronaviruses who is a microbiology professor at the University of Colorado in Denver, is that it is unlikely the SARS virus would mutate quickly into new, possibly even more infectious and deadly variants, despite speculation to the contrary. Like most viruses, coronaviruses, the viruses in the class that includes the one that causes SARS, tend to die if they mutate. That is why most disease vaccines, like those for polio, measles and smallpox, remain effective year after year. The flu, in which mutated viruses are infectious, is the exception, not the rule.

Coronaviruses also have molecular targets that should make them vulnerable to attack by drugs. It might also be possible to develop a SARS vaccine because people and animals who are infected with coronaviruses make antibodies that at least partially prevent them from being reinfected. The challenge will be to develop a vaccine that elicits antibodies in the respiratory tract and intestines, where they are needed.

Thus far, the World Health Organization has tried to stop SARS from spreading by issuing travel advisories, suggesting that people avoid going to Hong Kong, Beijing, Guangdong and Shanxi provinces in China. The health organization also is advising that patients and those who came into close contact with them be quarantined. But the virus has continued to spread.

America has been lucky


In the United States, there are just 39 probable cases of SARS and no deaths, a situation that Dr. Julie L. Gerberding, the director of the Centers for Disease Control and Prevention, attributed to good luck.

Scientists are asking if the SARS virus has an animal host. Coronaviruses are extremely common: Two different coronaviruses cause 15 percent to 30 percent of the colds in people, and other coronaviruses cause serious problems for farmers when they infect pigs, chickens and cows.

But the SARS virus was a surprise, Holmes said. Not only was its genetic sequence very unlike that of any other coronaviruses, but it had so many minute differences from known viruses that it seemed to have split off long ago, quietly evolving in some as yet unknown animal species. It does not appear to have previously infected humans, she said. When, in preliminary studies, investigators tested blood from blood banks, they saw no evidence that people had antibodies to the virus. That would have been a sign of previous infections.

Holmes said that the SARS virus' genetic sequence does not allow her even to guess about what animal it came from. But, she predicted, that mystery will be solved.

"We will see a big hunt for the original host," Holmes said. Researchers are set to take blood from birds and mammals in southeastern China, where the epidemic began, and look for SARS antibodies. Then they will try to isolate the virus, which might prove difficult. Most coronaviruses won't grow in the lab. One group, the human coronaviruses type 2, when first isolated, would grow only in cultures of the human fetal tracheal organ, Holmes said.

The SARS virus is unusual in this respect: It readily is isolated from patients and grows in standard laboratory cells -- which should allow scientists to isolate it from animals that harbor it.

As Holmes said: "That is wonderful. It is a gift from God. Otherwise, we would still be trying to figure out what it is."

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