SARS CAUSE FOUND
Experiments in monkeys confirm coronavirus is behind deadly disease
A previously unrecognized coronavirus causes the highly contagious disease known as severe acute respiratory syndrome (SARS), the World Health Organization (WHO) announced last week. That finding, paired with the sequencing of the virus's genome, should lead within weeks to sensitive and selective diagnostic tests for the deadly disease. But effective drug treatments are still months or years away, scientists acknowledge.
|CROWN JEWEL The distinctive halo appearance under the microscope gives coronaviruses their name.
"The pace of SARS research has been astounding," said David L. Heymann, executive director of WHO's communicable diseases programs. "Because of an extraordinary collaboration among laboratories from countries around the world, we now know with certainty what causes SARS."
The pathogen is a member of a family that includes a virus responsible for about a third of all common colds. Like other RNA viruses, coronaviruses are prone to mutate rapidly.
The coronavirus is one of a number of microorganisms isolated from SARS patients that have been under intense investigation since shortly after the disease was identified in early March. But only the coronavirus has now been found to satisfy the so-called Koch postulates, the criteria required by infectious disease experts to prove that a particular agent causes a specific disease.
"We decided to do an experiment in monkeys," Albert D. Osterhaus, head of Erasmus University's National Influenza Center in Rotterdam, the Netherlands, told a press briefing. "The animals infected with the coronavirus alone developed full-blown disease. They developed clinical symptoms, and they also developed the pathological lesions that are identical to what we have seen in people who have died from SARS."
Equally important, researchers at the British Columbia Cancer Agency, Vancouver, and at the Centers for Disease Control & Prevention (CDC), Atlanta, finished sequencing the genome of what now is to be known as the SARS virus. Each team completed its work in less than two weeks and has made its data public.
CDC's virus sequence differs from the Canadian sequence by only about 10 base pairs out of approximately 29,000, according to CDC Director Julie L. Gerberding. The sequence "clearly is consistent with a brand new virus in the family of coronaviruses," she said. But it hasn't cleared up the mystery of the virus's origin.
Having the sequence, however, will allow researchers to rapidly develop highly specific "primers"--strings of nucleotides--for polymerase chain reaction (PCR) diagnostic tests. And using other molecular biological techniques, scientists can now develop antigens for immunoassays without having to work with the infectious virus.
The findings also will help in identifying treatments and vaccine strategies. The U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Md., for example, will be screening 2,000 FDA-approved drugs for their activity against the SARS virus. But compared to diagnostics, concedes CDC's James Le Duc, "for therapeutic interventions, we are much, much further behind."
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