Exotic Market Yields a SARS Clue

Human-like virus found in Chinese animals

THURSDAY, Sept. 4, 2003 (HealthDayNews) -- It was just your typical live-animal food market in Shenzhen, China, with a palm civet here, a raccoon-dog there on display for the benefit of chefs, but it provided an important hint about the way an innocuous virus that lives peacefully in the human respiratory tract became the deadly virus SARS, researchers say.

Swabs from two Himalayan palm civets, members of a cat-like family, turned up a coronavirus resembling one that is carried by many humans but does no harm, scientists at the University of Hong Kong report in the Sept. 5 issue of Science. The virus was also found in a raccoon-dog and a ferret badger from the same market, and in some employees at the market.

Although the workers showed no signs of illness, the discovery "indicates a route of interspecies transmission" that created the severe acute respiratory syndrome virus, the report says.

"The concept here is that we know that coronaviruses are mutable," says Dr. Philip Tierno, director of clinical microbiology and immunology at New York University Medical Center and author of The Secret Life of Germs.. "But it was not known previously that animal and human strains could recombine to become more profoundly infective that the human strains we knew in the past."

The animal market was a logical place to look, the Hong Kong researchers explain, because the first cases of SARS, reported last November, occurred in restaurant workers from that region who handled wild mammals regarded as exotic foods. The Shenzhen market had a variety of species, held individually in small wire cages, that came from different regions of China.

"The Chinese lay out animals in open markets and sell for food animals we wouldn't eat, and that cohort together," Tierno says. "You have humans working in close proximity with these animals. If an animal is slaughtered, viruses can spread from animal to human."

Genetic analysis shows a family resemblance between the human and animal coronaviruses, the report says, although the human SARS virus is missing a large segment found in the animal virus.

The discovery indicates that the open-air markets are places where SARS-like animal viruses can "amplify and transmit to new hosts, including humans, and this is critically important from the public health point of view," the researchers write.

But it isn't clear that any of the virus-carrying animals in that market were the original source of the virus, they say. It is conceivable that they were all infected "from another, as yet unknown animal source, which is in fact the true reservoir in nature."

Much more work in markets, in the wild and in laboratories "will help to better understand the animal reservoirs in nature and the inter-species events that led to the origin of the SARS outbreak," the researchers say.

Meanwhile, a report by a panel of Central Intelligence Agency experts warns that while the SARS outbreak has been contained after infecting more than 8,400 people worldwide and causing about 815 deaths, the disease could re-emerge this winter, the time when respiratory diseases are most likely to spread.

"SARS has not been eradicated," says a report prepared by the National Intelligence Council to CIA Director George G. Tenet. "We remain vulnerable."

If the disease takes hold in Asian or African countries with inadequate health-care systems, it could cause more deaths than the first outbreak, the experts warn.

A quick response to contain the disease is necessary because "currently, SARS has no vaccine, no effective treatment and no reliable point-of-care diagnostic test," they say.

The U.S. Centers for Disease Control and Prevention says it plans to have a better SARS surveillance system in place this year.

More information

Everything you need to know about SARS is available from the U.S. Centers for Disease Control and Prevention or the World Health Organization.

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