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Scientists map suspected SARS virus genome

U.S. cases number 193

Dr. Julie Gerberding, director of the U.S. Centers for Disease Control and Prevention
Dr. Julie Gerberding, director of the U.S. Centers for Disease Control and Prevention

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Researchers in Canada and the United States say they have sequenced the genome of the virus thought to cause SARS. CNN's Glen Van Zupthen reports. (April 15)
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• Frequently Asked Questions: SARS 
• Map: SARS cases 
• Special report: SARS: Mystery illness on the move 
• Country breakdown: Suspect and probable cases of SARS 


Suspect case: A person who develops high fever (greater than 38 C / 100.4 F) and respiratory symptoms such as cough, breathing difficulty or shortness of breath, within 10 days of

1) having had close contact with a person who is a suspect or probable case of SARS.
2) having traveled to or resided in an affected area.

Probable case:  A suspect case with chest X-ray findings of pneumonia or respiratory distress syndrome.

ATLANTA, Georgia (CNN) -- Researchers in Canada and the United States, working independently, announced they sequenced the genome for the suspected cause of Severe Acute Respiratory Syndrome.

Researchers can use the information "to begin to target antiviral drugs, to form the basis for developing vaccines, and to develop diagnostic tests that can lead to early detection," said Dr. Julie Gerberding, director of the U.S. Centers for Disease Control and Prevention.

Already, a number of laboratory tests look promising, Gerberding said.

The mystery illness, which appears to have originated in China late last year, has spread to 21 countries, infecting 3,169 people and killing 144, according to the World Health Organization.

Computers at the British Columbia Cancer Agency in Vancouver completed work Saturday on the coronavirus, a new form of which is thought to cause SARS, the agency said.

Gerberding told reporters Monday: "Today, CDC has followed suit and has published the sequence of the virus."

"This is a huge step forward in the fight to control the spread of SARS," said Dr. Caroline Astell, projects leader at the Genome Sciences Centre.

Researchers collaborate

British Columbia Cancer Agency and CDC researchers were among many at 11 laboratories worldwide who have been collaborating in the effort to identify the cause of SARS and devise a vaccine or a treatment.

The labs have been focusing their efforts on a new form of coronavirus. Other forms of the virus are responsible for the common cold.

CDC looked at virus taken from an Asian patient and the Canadian center tested virus taken from a Canadian, Gerberding said.

Of approximately 29,000 nucleotides (basic units of DNA) sequenced by each group, the two centers differed by just 10 base pairs, a "trivial" difference, and one that suggests they came from a common source, she said.

In each case, the results are "consistent with a brand new virus in the family of coronavirus."

No proof yet

The virus sequences were not similar enough to coronavirus found in animals to determine where the newly recognized disease may have come from, she said.

For CDC, completion of the sequence just 31 days after the disease agency identified SARS as a problem is "a scientific achievement that I don't think has been paralleled in our history," Gerberding said.

But researchers have still not proved that the coronavirus is the cause of the disease.

To do that, they need an animal model to show that infection with the coronavirus results in the illness. Researchers in the Netherlands, working with primates, have made progress toward finding an animal model, Gerberding said.

Once an animal model is found, it would also be used to test which drugs or vaccines might be effective against the disease.

Army testing antiviral agents

Though no treatment has proven helpful, the U.S. Army is testing antiviral agents donated by pharmaceutical companies to see if any of them kills the virus, Gerberding said.

The antiviral agent Ribavirin initially stirred optimism when anecdotal reports found it helpful, but follow-up studies have yielded only "discouraging results," she said.

Gerberding predicted it would take far more time to devise a vaccine than it took to sequence the coronavirus: "I think it would be naive to say we'd have it in under a year."

Cases in the United States

So far, 193 suspected cases of SARS have been identified in the United States, none of them fatal. Fifteen involve transmission from patients to family contacts and five to health care workers, Gerberding said.

Protection is critical to stemming the worldwide spread of the disease. Visitors and hospital workers who care for suspected SARS patients must wear heavy-duty respiratory masks, the type used to protect from tuberculosis, she said.

But she urged people to use common sense in responding to some advertisements that offer putative protection, such as air purifiers.

"Separating help from hype is a very difficult challenge in the absence of all the data we'd like to have," she said. "There is no evidence that wearing commercial and sometimes expensive air purifiers adds anything to the safety."

Basic hygiene urged

Instead, she recommends people practice basic hygiene, like frequent hand washing, and avoid droplets from infected people.

Though containment procedures appear to be working in Taiwan, Canada and the United States, they have not halted the spread of the disease in Hong Kong, China and Singapore, she said.

Predicting the course of the disease is an imprecise exercise, she said.

"In the best-case scenario, we would see the virus go away," she added. Such an outcome is "not totally implausible as we enter summer months in the northern hemisphere, but it's unrealistic to count on that."

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