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Viral DNA Match Spurs China's Civet Roundup

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Science  16 Jan 2004:
Vol. 303, Issue 5656, pp. 292
DOI: 10.1126/science.303.5656.292

SARS is back. The deadly respiratory virus has been confirmed in one patient—now recovering—in China's southern province of Guangdong. And three other possible cases in the area are under observation. But international health experts say that, in contrast to last year, China is responding aggressively. Officials are quickly isolating patients who develop SARS (severe acute respiratory syndrome), identifying their recent contacts, and sharing information with outside groups such as the World Health Organization (WHO). “This is exactly what [China] should be doing,” says WHO spokesperson Dick Thompson.

Hoping to cut off the source, Guangdong Province officials also ordered a sweep through farms and food markets to find and kill animals that may harbor the SARS virus, including masked palm civets and raccoon dogs. Some outside observers were initially skeptical of the cull, warning that it could spread the virus if not strictly supervised. But the purge is strongly supported by some researchers, such as a group at the University of Hong Kong (HKU), which provided key evidence that set the animal roundup in motion. The group's leader, HKU virologist Guan Yi, says that the team established a monitoring program in animal markets that identified a viral DNA sequence in civets that precisely matched a sequence found in the confirmed SARS patient.

Clean sweep.

Workers spray cages in a Guangzhou market and remove animals thought to harbor the SARS virus.

CREDIT: CHANG FENG/EPA/AP

Guan thinks the surveillance and intervention were critical: “Maybe we have been successful in avoiding a second outbreak.” WHO epidemiologist Andrea Ellis is more cautious. Although Guan's team made an “important contribution,” she says, “we need to keep in mind that other animals could be involved.” She warns that it is too early to celebrate.

China's second battle with the virus began in late December after Chinese authorities announced that they had identified a suspected SARS case; they confirmed the diagnosis on 5 January. Since then they have identified three more suspected cases, still pending confirmation. They are all in Guangdong Province—which borders on Hong Kong—where SARS first emerged in late 2002.

The decision to slaughter an estimated 10,000 civets and a lesser number of other animals in Guangdong's markets came on the same day that China confirmed its first SARS case of the 2003–04 winter. But it is not the first time that Guan and his colleagues in the microbiology department at HKU have helped authorities make a tough call. Since the early 1990s, the group has cooperated with Robert Webster, a flu expert at St. Jude Children's Research Hospital in Memphis, Tennessee, on a program funded by the U.S. National Institutes of Health to monitor viral strains circulating in chickens that could threaten humans. To eliminate a flu that proved fatal to humans in 1997, the group advised Hong Kong to slaughter all the chickens in the territory; Hong Kong followed the advice.

Last spring, Guan was the first researcher to find the SARS virus in civets and two other species sampled at Guangdong's live animal markets (Science, 30 May 2003, p. 1351). Chinese authorities promptly banned sales of those animals until human cases stopped appearing and the SARS scare passed last summer.

Virus hunter.

A team led by Guan Yi of the University of Hong Kong found a match in viral DNA from a SARS patient and a civet.

CREDIT: D. NORMILE

Convinced that the live animal trade still posed a risk, Guan started systematically screening civets and other exotic species in Guangdong's markets last October in cooperation with the Guangdong Center for Disease Control and Prevention. They found, he says, “many civets with high [SARS] viral loads.” Skeptical provincial authorities hesitated to take action. But they ordered a cull, Guan says, after the researchers showed that critical genetic sequences were nearly identical in both the human and the civet virus isolates.

“This time there is no doubt that the [virus] came from the animal,” says Webster. Even though the patient claims never to have eaten or even seen a civet, and none of his contacts show evidence of infection, Webster says, he could have been infected indirectly by virus from an animal.

Public health experts around the world were generally supportive of moves to get civets out of the markets. “Banning game animals [from the markets] is what should be done,” says Albert Osterhaus, a virologist at Erasmus University in Rotterdam, the Netherlands.

At the same time, most scientists would like to see more efforts to define the geographical distribution of infected animals and trace the virus back to its presumed animal reservoir, which may be localized. “Animals in different areas may not all have caught the SARS virus,” says Xu Jianguo, director of the National Institute for Communicable Disease Control, a part of the national Center for Disease Control and Prevention in Beijing. His group is now working with other provinces to confirm where the virus is endemic and where it isn't as well as to search for the reservoir. “This is not the end of the story, it's [just] the beginning,” Webster says.

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