Scientists have confirmed the genomes of two different strains of the virus thought to be responsible for Severe Acute Respiratory Syndrome (SARS), which has so far claimed 391 lives worldwide. As part of an international endeavor to stop the spread of SARS, most of the data had previously been made public as soon as it became available. Now independent researchers have reviewed the genetic sequences. Two papers describing the findings were released yesterday by the journal Science. Researchers hope that knowledge of the full virus genome will help efforts to contain the disease by aiding development of diagnostic tests, therapies or vaccines.
An international team led by Paul A. Rota of the Centers for Disease Control and Prevention (CDC) sequenced a strain of the virus recovered from the respiratory tract of a patient who died from the disease after contracting it in Hanoi. The analysis of this so-called Urbani strain confirmed that the virus belongs to the coronavirus family and that it is "distinct from all known coronoviruses," says study co-author Steven Oberste of the CDC. The genome of this strain has the same overall structure as that of the three currently recognized classes of coronavirus, but there were significant differences in the amino acid structures of individual proteins. "Unfortunately," Oberste notes, "the new analysis doesn't tell us a lot about the origins of the virus."
The second genomic sequence was completed by a group of Canadian researchers led by Marco A. Marra of the British Columbia Cancer Agency Genome Sciences Center. They analyzed the 29,751 bases that make up the genome of a viral strain taken from a patient in Toronto, the city hardest-hit by SARS outside of Asia. According to Mark Pallansch of the CDC, the two genomes are very similar despite coming from two distant locales. Notes Barry R. Bloom of the Harvard School of Public Health in an accompanying editorial, "the lesson here is that it is time to support an international war on disease."
Of particular interest to researchers hoping to develop new methods of treatment for SARS are the sections of the genome responsible for protein production. Both collaborations identified genes for four proteins essential to the virus's ability to enter host cells and replicate. But questions remain over whether the virus acts alone in causing the disease. Frank Plummer, the science director general of Health Canada's National Microbiology Lab in Winnipeg, told an international conference on SARS in Toronto that the new coronavirus has only been detected in 40 percent of the people who have SARS in Canada. Furthermore, specimens from 14 percent of patients under observation because they have potentially been exposed to the disease--but who do not meet the clinical case definition of SARS--have been found to contain the mysterious virus.