Gene Study Narrows Source Of SARS

New Scientist ^ | 9-4-2003 | Emma Young

[blam]

Gene study narrows source of SARS

19:00 04 September 03

NewScientist.com news service

The SARS-like virus found in a food market in Guangdong, China jumped from animals to people - and not the other way around - suggests new research.

The study represents an important step in tracing the original source of the virus. However, the work still leaves many important questions about the route of transmission of the SARS virus to people unanswered.

In May, the researchers, led by Yi Guan at the University of Hong Kong, revealed initial results of tests on a SARS-like coronavirus isolated from market animals including Himalayan palm civets. Their rough whole genome comparison with the virus that causes SARS in people (SCoV) found that the two were almost identical. But subsequent work on specific gene sequences has now revealed a few significant differences, says Yi.

It is not yet clear what the biological importance of these genetic differences might be. Some people who traded or slaughtered wild animals in the market tested positive for antibodies to this close relative of SCoV. But, like the animals, the people were not sick and have not reported symptoms of SARS during the past six months.

It could be that sequence variations make the SCoV more virulent, says Edison Liu, director of the Genome Institute of Singapore, which has worked on sequencing the SARS virus. But more work is now needed to find out.

Family tree

The detailed genetic analysis shows that the market and SCoV viruses come from different sub-lineages of the same family tree. And it also shows that a strain of the market virus that infected one civet and the raccoon dog were genetically almost identical, suggesting that one animal might have transmitted the virus to the other within the market.

The team found deletions in the sequence of SCoV from human patients, compared with the market cluster. "The loss of DNA fragments is more commonly seen upon passage from animal to man, than a gain in the sequence," says Liu. Yi thinks this is convincing evidence. "This research confirms that SARS is a zoonotic disease - that's quite clear," he says.

The findings suggest that civets could be symptom-free carriers of the virus that, with very small modifications, causes SARS in people. But whether civets might be a natural reservoir for the virus, or caught the virus from some other animals is not known.

Detecting a reservoir, and identifying any further animals that can be infected with these close relatives of the SARS virus will be important for preventing or controlling a future outbreak of the disease.

Further research is also needed to understand the significance of finding antibodies to the market viruses in some workers, says Yi. Whether these people were the intermediaries that carried the virus to other people is not yet known, he says.

But the researchers say their work does at least suggest that, as suspected, wild animal markets provide a venue for the animal SCoV-like viruses to transmit to new hosts, including humans. As they write in their paper in Science: "This is critically important from the point of view of public health."

Journal reference: Science (DOI: 10.1126/science.1087130)

Emma Young

[blam]

I'm not sure if this tells us any more than we already know.

[blam]

FYI.

[Lessismore]

http://www.sciencemag.org/feature/data/sars/index.shtml#animals

Tracking Down the Animal Hosts of SARS

[aristeides]

I'm not sure if this tells us any more than we already know.

That's just what I was wondering, reading this.

[ex-Texan]

There was a report that linked SARS to rats. By that I mean ratus ratus type rats. The Chinese have very strange preferred food groups.

[fatima]

aristeides,Thank you.

[Judith Anne]

I echo that: Aristeides, thank you.