|Exotic market animals likely source of SARS
Evidence of the deadly SARS virus has been discovered in three exotic animal species being sold live in a Chinese food market. The revelation is highly significant as it may allow SARS to be stopped at source and may help in the development of diagnostic tests.
The virus found is "almost identical to the human SARS virus", according to Klaus St? SARS basic science research director at the World Health Organization.
The virus itself was uncovered in six civet cats and one raccoon dog and antibodies to the virus were found in a badger known as the Chinese ferret badger. The researchers, from Hong Kong and mainland China, had sampled over 25 animals from a local food market near a laboratory in China's Guangdong province.
It is "highly likely" that the virus jumped from the animals to humans, said Kwok-Yung Yuen, head of microbiology at the University of Hong Kong. He unveiled the results of the pilot study, conducted with the Shenzhen Centre for Disease Control and Prevention, on Friday.
The exotic mammals are considered as culinary delicacies in Guangdong, where the killer virus first surfaced in November 2002. The disease spread rapidly across the globe, and has now caused over 8100 infections and nearly 700 deaths.
Yuen and colleagues found evidence of the deadly virus in three of the eight wild animal species tested. The civet cats were of the species Paguma larvata, known as the Himalayan masked palm civet. The coronavirus was isolated from its faeces and respiratory secretions.
"Genomic analysis suggests that these animal isolates are precursors to human isolates," says a statement from the University of Hong Kong. "The finding has extremely important implications for the control of this infection."
Additional tests confirmed the close similarity of the virus found in the animals and that found in humans, said St? during a WHO telephone press briefing to discuss the "exciting" results.
He said that blood serum from the infected animals successfully inhibited the growth of human SARS coronavirus in the laboratory. Blood serum from humans with SARS also inhibited the animal virus in the lab, "another strong indication these viruses are very, very closely related," says St?
Chain of transmission
Fran║Ys Meslin, co-ordinator of zoonoses at the World Health Organization, noted that the species implicated might not be the "ultimate source" of SARS but "part of the chain of transmission".
Such chains can amplify the effects of a virus. For example, Nipah virus, emerged in Malaysia in 1999, killing over 100 people. It jumped from pigs to humans, but the virus originated in bats. Its transmission through the pigs enhanced its virulence.
Meslin said how the SARS might transfer to humans from exotic market animals was unknown. But he added that as the virus was found in body fluids it was likely to infect market traders handling infected animals. Eating infected animals seems less likely route, he says, based on evidence from other animal diseases.
Trade in these animals for human consumption should stop, said the WHO officials, in order to stop the spread to humans. WHO spokesman Dick Thompson said one Chinese official had already indicated that China would be stopping the trade.
In a separate development, two new epidemiological studies have concluded that SARS is contagious enough to cause a global pandemic, if uncontrolled. The researchers tried to calculate how fast SARS spreads, and what might stop it, by analysing data from Hong Kong, Singapore and other outbreaks.
Both studies, released by Science on Friday, found that in the absence of isolation and other control measures, each SARS case causes on average two to four more cases. "If uncontrolled, it would infect the majority of people wherever it was introduced," conclude the WHO's Chris Dye and Nigel Gay, in a commentary on the work.
On the other hand, SARS is not so wildly contagious as to be uncontrollable - each new case of smallpox, for example, causes 6.5 new cases. Both teams conclude that the spread can be checked by basic measures such as isolating patients and quarantining contacts.
However, Dye and Gay note that a few people, dubbed "super-spreaders" shed large amounts of virus and have been known to infect up to 300 people by themselves. That results in a different type of epidemic from one caused by people who infect only two to four others.
Original source: NewScientist.com
Submit by CEIN News on 5/27/2003