Posted on 06/02/2003 8:42:22 PM PDT by Neuromancer
Virus detectives seek source of SARS in China's wild animals
Researchers investigating the source of severe acute respiratory syndrome (SARS) have turned their attention to the wild-animal markets of southern China. The move follows reports that workers and animals at the markets show high rates of infection with coronaviruses, the family to which the virus believed to cause SARS belongs.
The possible link to wild animals emerged on 23 May 2003, when a team from the University of Hong Kong revealed that a coronavirus resembling the SARS virus had been isolated from 6 masked palm civets (_Paguma larvata_) and a raccoon dog (_Nyctereutes procyonoides_) in a market in Shenzhen, in the southern Chinese province of Guangdong. Antibodies against the virus were also found in a Chinese ferret badger (_Melogale moschata_) from the same market. Although the virus is not the same as that believed to cause SARS -- a member of the Hong Kong team describes it as "genetically very close, but not identical" -- 5 out of the 10 civet handlers at the market had antibodies against the SARS virus in their blood. A Chinese government team has since released results showing that 66 out of 508 animal handlers tested at markets in Guangdong had antibodies against the SARS virus.
Microbiologist Kwok-yung Yuen, who led the Hong Kong team, notes that in the general population, the level of antibodies against the SARS virus is much lower. "This suggests that the virus is jumping from wild animals to humans," he says.
Because the animal virus is similar to the SARS virus, but different from other coronaviruses, it is now a prime suspect in the hunt for the origins of SARS. The likelihood that the virus is moving the other way -- from humans to animals -- is diminished by ongoing work on genetic sequences of the 2 viruses. These analyses suggest that the animal version has an extra stretch of 29 nucleotide bases. "Viruses tend not to gain stretches of nucleotides when they jump across species," says Klaus Stoehr, a SARS expert at the World Health Organization (WHO) in Geneva.
But uncertainties remain over the exact source of the virus. Only 6 civets were present in the market, and the fact that they all had the virus suggests that they were infected recently. "They could have gotten it from another animal during transport to the markets," says Zhang-liang Chen, a molecular biologist and president of the China Agricultural University in Beijing. Chen's group did not find the SARS virus in samples from 8 civets taken from other markets and in the wild in Guangdong.
[Perhaps the most significant aspect of the above report from Nature is that some animals in other markets or in the wild have tested negative for the SARS coronavirus. So it is possible that the animals in the market in Shenzhen may have been infected from an unknown animal or human source. A potential animal reservoir and the direction of transmission of the virus are still unresolved issues.
Dr. Henry L Niman, (Instructor in Surgery (Bioengineering) Harvard Medical School ) has observed that, irrespective of the biological data, the molecular story remains clear at this time. 16 of the 17 available SARS coronavirus genome sequences have the same 29-nucleotide deletion (the GZ01 sequence being the single exception), whereas the genome sequences of at least 2 civet cats (and the GZ01 sequence) have the same corresponding 29-nucleotide insertion. It is clear, however, that more data are required before the biological relevance of this 29-nucleotide deletion/insertion can be assessed.
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