Chinese animal traders carried antibody to SARS virus

Oct 16, 2003 (CIDRAP News) – Chinese investigators have found that animal traders in Guangdong Province were more likely to carry an antibody to the SARS (severe acute respiratory syndrome) coronavirus than other local groups were, supporting the belief that the virus might have come from animals.

However, the study did not pinpoint the original natural reservoir for the virus or make clear which animal might have transmitted it to humans, according to the report from the US Centers for Disease Control and Prevention (CDC). The report appears in the Oct 17 issue of Morbidity and Mortality Weekly Report.

In the study, provincial and city health officials recruited and took blood samples from traders in three animal markets in Guangzhou, Guangdong Province, last May. Samples also were collected from three control groups: healthcare workers involved with SARS control in two city hospitals; public health workers in the Guangdong Center for Disease Control and Prevention; and healthy adults visiting a clinic for routine physical exams. None of the subjects had SARS or atypical pneumonia during the Guangdong outbreak.

The investigators used enzyme-linked immunosorbent assay (ELISA) to test the blood samples for IgG antibody to the SARS coronavirus. Thirteen percent (66 of 058) of the animal traders had the antibody, compared with 2.9% (4 of 137) of the hospital workers, 1.6% (1 in 63) of Guangdong CDC workers, and 1.2% (1 in 84) of the healthy adults, according to the report. The difference between the animal traders and the overall control population was significant (P<0.01), but the differences among the three control groups were not.

Among the animal traders, the antibody was most common among those who primarily sold masked palm civets, with 73% of them carrying it. For traders of other animals, the percentages who had antibody were as follows: wild boar, 57%; muntjac deer, 56%; hare, 46%; pheasant, 33%; cat, 19%; other fowl, 12%; and snake, 9%.

The report says the findings are "consistent with the hypothesis that SARS-CoV crossed the species barrier from animals to humans." Other evidence for that view includes a previous finding that sequences of coronavirus isolates from bats, monkeys, masked palm civents, and snakes matched or nearly matched SARS coronavirus isolates from humans.

However, the findings do not identify the virus's natural reservoir or show which animal species passed it to humans, the article says. It adds that only two SARS patients in Guangdong Province, which had about 1,500 probable cases, were identified as animal traders. In contrast, an analysis of early Guangdong cases that were not linked with other SARS cases showed that food handlers were overrepresented.

"Efforts to identify a possible animal reservoir for SARS might benefit from prompt attention to collecting detailed histories from any future SARS patients regarding animal and other environmental exposures and initiating tracebacks to animal supply sources," the report concludes.

CDC. Prevalence of IgG antibody to SARS-associated coronavirus in animal traders—Guangdong Province, China, 2003. MMWR 2003 Oct 17;52(41):986-7 [Full text]

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