SARS spread from live markets, but when?

BEIJING––Blood tests indicate that about 1% of the children in 17 provinces of China were exposed to Severe Acute Respiratory Syndrome before the outbreaks of 2002-2003 that hit 24 of the 31 provinces.

Evidently passing from animals sold in filthy live markets to humans working in food preparation, and then spreading from human to human, SARS eventually killed 916 people in 32 nations, with about 650 of the deaths occurring in mainland China and Hong Kong.

The blood study was conducted by the Beijing Military Zone Air Force Logistics Sanitation Unit, using samples taken from healthy children before SARS appeared.

In a parallel study, the Beijing Capitol Pediatrics Research Institute found that among 77 children hospitalized for various reasons in 2001, 42% had antibodies to SARS. Among 92 children hospitalized during the SARS outbreak, 40% had the antibodies but none had SARS symptoms.

Both studies indicate that the coronavirus responsible for SARS was already widely distributed among the human population at least among children well before it turned deadly. The findings may explain why relatively few children developed the deadly strain of SARS, but confounds the mystery of how SARS originated, since children are also less likely than adults to consume wildlife products.

One possibility is that children receive antibodies to SARS via mothers milk. Chinese women may be more likely than men to be exposed to SARS through food preparation and tending farmed wildlife, but men are the major wildlife eaters.

A Beijing University Hospital study meanwhile confirmed that SARS is not easily transmitted to people who take precautions against the it, finding no evidence that SARS ever passed from patients to the health workers who treated them.

The three new studies by Beijing institutions were released three weeks after Hong Kong University gene sequencing expert Guan Yi and team reported in Science that they discovered antibodies 99.8% identical to the SARS-like virus antibodies found in four masked palm civets and a raccoon dog last May in eight of 20 wildlife traders, three of 15 slaughterers, and one of 20 vegetable sellers tested at the Guangdong market where the exposed animals were found.

None of the market workers actually had SARS.

Our investigation clearly shows that the SARS-like virus comes from the SARS-like virus in the wild animal market, Guan Yi said. But we still have no direct evidence that the viruses in the markets can attack humans directly.

Harvard Medical School scientific reviewer Henry Niman, MD., told Mary Ann Benitez of the South China Morning Post that the Guan Yi team also found a direct link between a masked palm civet and two infected Guangdong health workers.

In mid-August 2003, four months after suspending wildlife sales, the China State Forestry Administration reauthorized the sale of 54 species of wildlife as live meat or pets, providing that the animals are captive-raised.

“Lifting the ban was a bit reckless,” Niman said.

Maria Cheng, spokesperson for the Beijing office of the World Health Organization, agreed with Niman that, “Perhaps it would have been better to wait until we had more information for China to lift the ban” on wildlife consumption.

Hong Kong legislator for the medical sector Lo Wing-lok and legislator for food and hygiene Fred Li Wah-ming called for the ban to be reimposed.

Wary of protests that broke out in Guangdong in early summer, however, led by unemployed wildlife traders, an anonymous mainland State Forestry Administration official reportedly dismissed the new findings as inconclusive.

French epidemiologist Francois Moutou told Agence France-Presse in August that a 14-member team of United Nations and Chinese experts had found SARS-like viruses in a wide range of birds, reptiles, and mammals at markets and farms in south China. Their conclusions, however, have not yet been scientifically reported.

(October 2003)