[an error occurred while processing this directive]
BBC News
watch One-Minute World News
Last Updated: Friday, 30 January, 2004, 00:50 GMT
Science mapping Sars 'evolution'
The coronavirus: Mutated rapidly
The origins of Sars have been made clearer by a genetic study that traces it back to wild animals in China.

As scientists worry about the potential for bird flu to one day become a major killer, the study shows how Sars "jumped" to humans a year ago.

More than 800 deaths and 8,000 cases resulted from Sars outbreaks in Hong Kong, China and Canada.

Researcher Dr Chung-I-Wu, from Chicago University, said it was "disturbing" to watch it gradually gain virulence.

The current Avian influenza outbreak in the far East is related to Sars only in demonstrating how so-called zoonotic diseases in animals can cross to become a threat to human health.

Although not easily passed from human to human, Sars caused a life-threatening respiratory infection in many cases, and experts are braced for its return this winter.

Researchers are now convinced that Sars made that jump in late 2002 in the Pearl River Delta in the Guangdong Province of China.

Cross checking

They compared the genomes of viruses isolated early in the emergence of Sars, and compared them to isolates from later victims of the virus.

What we see is the virus fine-tuning itself to enhance its access to a new host - humans
Dr Chung-I Wu
University of Chicago
This showed how the coronavirus which causes the illness adapted to become better at living in humans.

Two "genotypes" dominated the early phase of the epidemic - these were roughly comparable with coronavirus isolates taken from animals in a market in Shenzen.

In the middle phase of the outbreak - including the "super-spreader" event at a hospital in Guangzhou in January 2003 - during which case numbers multiplied, the genetic makeup of the virus had already shifted.

Different versions of the coronavirus predominated - with one in the hospital and another emerging in Hong Kong.

Within a month, another genotype had emerged, which persisted to the end of the outbreak in August.

Cell key

When scientists examined levels of gene mutations in one particular gene - called spike - which was thought to be involved in the ability of the virus to enter cells, it was found to be undergoing rapid mutations at the start of the outbreak, which slowed down after it had refined its ability to infect humans.

Sars has caused widespread fear
Dr Chung I-Wu said: "What we see is the virus fine-tuning itself to enhance its access to a new host - humans.

"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.

"The genetic fingerprints add a whole new layer to our understanding of the course of events in this epidemic."

Avian flu
14 Jan 04  |  Medical notes
Human trials for Sars vaccine
19 Jan 04  |  Health
Timeline: Sars virus
17 Jan 04  |  Asia-Pacific

The BBC is not responsible for the content of external internet sites


News Front Page | Africa | Americas | Asia-Pacific | Europe | Middle East | South Asia
UK | Business | Entertainment | Science/Nature | Technology | Health
Have Your Say | In Pictures | Week at a Glance | Country Profiles | In Depth | Programmes
Americas Africa Europe Middle East South Asia Asia Pacific