THE unprecedented global research effort into SARS is paying off, with a spate of new discoveries. While not all are reassuring, some may help to improve treatments.
It turns out that the body鈥檚 immune response is to blame for SARS deaths, as it is in some other diseases. Ten days after the illness starts, antibody levels shoot up and levels of the coronavirus plummet, Malik Peiris of Hong Kong University has found. Then damage also starts showing up all over the lung.
This suggests that the damage is caused by an overstimulated immune system rather than uncontrolled replication of the virus itself, Peiris鈥檚 team concludes in The Lancet, online edition. They say that early on in the disease, doctors should focus on stopping the virus replicating, while later on the immune response needs to be dampened down, perhaps with the body鈥檚 own specific immune inhibitors. Doctors in Hong Kong have now stopped giving immunosuppressant steroids early on.
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Several potential treatments emerged this week. David Ho of the Aaron Diamond AIDS Research Center in New York announced that the drug enfluvirtide (Furzeon), which stops HIV entering immune cells, also keeps out the SARS virus, which might stop it replicating. And a modified version of an experimental anti-cold treatment might inhibit a protein-cleaving enzyme essential for SARS to replicate, according to Kanchan Anand at the University of Lubeck, Germany.
Better treatments are certainly needed to cut the death rate, which is far higher than first thought: up to 18 per cent in Hong Kong, according to calculations by Christl Donnelly of Imperial College, London. The World Health Organization now puts the fatality rate globally at 15 per cent.
In people over 60, the death rate jumps to 50 per cent. This is consistent with a disease in which the immune response kills, says Earl Brown of the University of Ottawa. In older people, the immune system can more easily go wrong: 鈥淵ou don鈥檛 hit the virus so well, but you hit yourself,鈥� he says. By contrast, children with SARS in Hong Kong did not die, Peiris reports, and didn鈥檛 have chills and aches characteristic of a 鈥渃ytokine storm鈥�, the kind of immune response that kills adults.
Most people infected so far have been in contact with other known cases, which suggests that SARS can be contained simply by quarantining contacts. But last week the WHO confirmed that the virus can persist on surfaces for at least a day. This would explain some mysterious cases in Taiwan and mainland China.
One surprise is that the SARS coronavirus appears relatively stable, rather than mutating rapidly as was expected. Viruses from different patients sequenced by Edison Liu of the Genome Institute of Singapore turn out to be remarkably uniform, and most of the variations observed so far probably occurred when the viruses were grown in culture.
Less encouragingly, a mutation in one of the spikes on the virus鈥檚 coat that help it invade cells has remained stable in the especially successful strain that spread from the Metropole Hotel in Hong Kong to Singapore, Canada and Vietnam. The team concludes that this spike may help the virus evade the immune system.
Overall, more than 7400 people have fallen ill with SARS and 552 have died. Vietnam and Canada appear to have halted the spread of the disease and the number of new cases is falling in Hong Kong. But it has spread to nearly every province in mainland China, and Taiwan is also battling to contain it. Vigilance is still needed, as occasional cases are also cropping up elsewhere. Just one infected person could spark another major outbreak if not spotted in time.