Secret Of SARS Virus's Lethal Mutation Unlocked By Scientists

Scientists have identified the stages in the evolution of the Sars virus that turned it from a simple animal infection into a lethal human disease.

A study of the genes of more than 60 Sars viruses has found that it took just three major changes to the virus's genetic material to transform it into a highly effective killer of people.

During the earliest phase of the epidemic the Sars virus infected about 3 per cent of those who came into direct contact with it, according to the study. Within a few months the proportion was 70 per cent.

Chinese scientists, working with a team at the University of Chicago, analysed the Sars virus from the early, middle and later phases of the 2002-03 epidemic. The researchers found that the first phase of the epidemic involved a virus virtually identical to that found in wild animals but it mutated to cause a second phase, during which the virus spread from human to human.

A final, third phase involved a further set of mutations that allowed the virus to stabilise and get accustomed to spreading still further within its new host species, said Chung-I Wu, professor of ecology and evolution at the University of Chicago. "What we see is the virus fine-tuning itself to enhance its access to a new host - humans. The virus improves itself under selective pressure, learning to spread from person to person, then sticking with the version that is most effective," Professor Wu said.

The findings, published in the journal Science, confirmed that Sars was an animal disease that had jumped the "species barrier" into man. But the study did not determine which animal was the natural "reservoir" for the virus.

In the early stages of the epidemic, in November 2002, there were about 11 seemingly independent cases of human Sars in the Pearl river delta area of Guangdong province in China. The scientists found that the rapid economic development of the area had led to "culinary habits involving exotic animals". Six of the 11 outbreaks involved people who had contact with wild animals.

During the middle phase of the epidemic the scientists discovered that there were changes to the Sars virus that enabled it to spread rapidly from person to person, accelerated by a "super-spreader" patient in a hospital in Guangzhou.

This phase, in January 2003, resulted in an outbreak of about 130 cases, including 106 patients who acquired the virus in hospital. A doctor at the hospital carried the virus to the Metropole Hotel in Hong Kong where the guests became infected and spread the virus across the world.

'SARS mutated into more infectious form'

January 30 2004 at 05:54AM
By Reuters
By Maggie Fox

Washington - The Severe Acute Respiratory Syndrome (SARS) virus fine-tuned itself to become more infectious as last year's epidemic spread across China, researchers reported on Thursday.

Early patients with SARS had a genetically form, very similar to that seen in civets, while the last patients in the epidemic had a slightly mutated form, the researchers said.

"What we see is the virus fine-tuning itself to enhance its access to a new host, humans," Chung-I Wu, a professor and chairperson of ecology and evolution at the University of Chicago, said in a statement.

'Early patients with SARS had a genetically form' "This is a disturbing process to watch, as the virus improves itself under selective pressure, learning to spread from person to person, then sticking with the version that is most effective."

This may explain why the virus became more infectious with time, Wu said.

The finding, published in the journal Science, supports the idea the virus leapt to people from animals and also should allow experts to understand the virus better.

SARS infected more than 8 000 people last year and killed nearly 800. This year, two people have been confirmed to have been infected with SARS and a third is considered a probable case, all in China.

The virus that causes the disease, marked by severe pneumonia, is a never-before-seen type of coronavirus. Coronaviruses cause the common cold in people and a range of infections in animals.

'SARS infected more than 8 000 people last year' Wu, Guoping Zhao of the Chinese National Human Genome Centre, and colleagues in China including at the Guangdong Centre for Disease Control and Prevention studied the spike protein on the virus, known to give the microbe its ability to infect.

In the first people infected it was virtually identical to viruses taken from civets, weasel-like animals valued for their meat and sold in markets in southern China.

As the virus spread more freely from person to person, it mutated slightly, apparently adapting itself better to live in humans. That was when the "super-spreading" occurred that made the virus so frightening, including the case of a doctor who infected several people at a Hong Kong hotel.

The virus then gradually evolved into a more stable genetic form toward the end of the outbreak, Wu's team reported.

They said the study should help researchers find a vaccine against SARS based on the spike protein.

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