Researchers have traced how the severe acute respiratory syndrome (SARS) virus evolved during the early stages of last year's epidemic, providing new clues about how the virus adapts to human hosts. The work offers hints about the best way to create a SARS vaccine, and it could help health officials predict when and where the virus will strike next.
SARS has claimed 774 lives worldwide. At its peak in February 2003, more than 50 new cases were being diagnosed each day. Within months, researchers had identified the virus, sequenced its genome, and stemmed its spread. SARS likely spread from masked palm civets, but nobody knows how the virus honed its weapons for attacking humans.
To find out, microbiologist Guo-Ping Zhao of the Chinese National Human Genome Center in Shanghai and 54 colleagues tracked the virus's evolution through the epidemic. First, they tracked down tissue samples from 22 patients infected during the early, middle, and late stages of the epidemic. Then they compared the genome sequences of these SARS strains with each other and with those from masked palmed civets to see how the virus mutated as it spread.
Early in the epidemic, an array of SARS strains were present, some with genetic fingerprints that resembled those of the civet virus. Early SARS strains included many variants of the virus's spike protein, which helps it adhere to host cells. As the epidemic progressed and the virus began rapidly infecting people in Hong Kong, fewer spike protein variants turned up. That suggested that the spike protein is key for infecting humans, Zhao's team reports online 29 January in Science.
The later, nastier strains also had mutations that disabled a mysterious SARS gene called Orf 8, suggesting that it too played an important role in infection. Together, the results mean that early SARS cases probably came directly from civets and that it will probably happen again. Indeed, the SARS strains from the three mild cases that have surfaced in China since December have a genetic fingerprint that looks more like that of the civet version. Given how the virus adapted last year, it's especially important to nip epidemics in the bud, Zhao says.
“This is a tremendous advance” in understanding exactly how SARS spreads from animals to humans, says virologist Kathryn Holmes of the University of Colorado Health Sciences Center in Denver. By identifying the altered proteins that enable the virus to infect humans, it could focus the efforts of vaccinemakers on those proteins and speed development of a SARS vaccine, she says.
Related sites
FAQs about SARS,
from the U.S. Centers for Disease Control and Prevention
SARS background and news
on the outbreak from the World Health Organization
)
)
)
)
)
)
)
)
)
)
)
)
