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SARS Genome Seems Stable
Edward R. Winstead

The genome of the SARS virus has not mutated significantly as the virus has spread around the globe.

Transmission electron micrograph of coronavirus OC43. Courtesy CDC.
The SARS virus is a type of coronavirus (above).

In the first of what could be many such studies, scientists have compared the genomes of SARS strains isolated from 14 patients. They found a relatively small number of genetic mutations among the strains, which suggests that the virus is stable and is not mutating at a high rate.

From the perspective of fighting SARS, the news is both good and bad. On the one hand, scientists may find it easier to develop vaccines against a virus with a stable genome than one that mutates frequently.

But a stable virus is unlikely to become less virulent on its own accord; the virus probably will not mutate and “lose” genes that make it deadly to humans. Indeed, genetic stability is an indication that the virus has adapted to living in the human host.

A team led by Edison Liu of the Genome Institute of Singapore sequenced the genomes of five related SARS strains from Singapore (the “index” case, three primary contacts, and one secondary contact). These five genomes were compared to nine others, isolated from patients in Canada, Hong Kong, Hanoi, Guangzhou, and Beijing.

Among the set of 14 strains, the team identified 129 DNA variations, including 16 that recurred. Some of the variants were associated with specific geographic regions; one group was linked to infections originating in the Metropol Hotel in Hong Kong.

Whether any of these common variants cause biological or clinical differences remains to be seen. But these and other variants could be used in future studies to track the spread of the disease. The study is published online in The Lancet.

The findings do not resolve the mystery of where and how did SARS arise. Solving this puzzle will require “a great deal of retrospective isolation and genomic sequencing of human and animal coronaviruses, especially in the virological hotbed of southern China,” write Earl G. Brown and Jason A. Tetro of the University of Ottawa in a commentary in The Lancet.

See related GNN articles
»SARS Genomes Unveiled
»SARS Genome Roundup

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Ruan, Y. et al. Comparative full-length genome sequence analysis of 14 SARS coronavirus isolates and common mutations associated with putative origins of infection. Lancet Published online May 9, 2003.
Brown, E.G. & Tetro, J.A. Comparative analysis of the SARS coronavirus genome: A good start to a long journey. Lancet Published online May 9, 2003.

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