Tests on workers strengthen SARS link between animals, humans

LONDON -- SARS antibodies found in workers who handled exotic animals at a market in southern China lend further support to the theory that the disease jumped from animals to humans, a World Health Organization scientist said Tuesday.

Last week, scientists reported they had found evidence of the SARS virus in three species of mammals for sale at a food market in Shenzhen.

Now, medical checks on 10 workers at the market found that five had at one time been infected with the SARS virus, without becoming severely ill. Experts say the findings strengthen the link between animals and humans.

The study, conducted by researchers at the University of Hong Kong in collaboration with the Shenzhen Disease Prevention and Control Center, found SARS antibodies in the blood of the five workers at Dongmen Market. Antibodies are disease-fighting chemicals tailored for specific bugs. They are evidence of a prior infection, but do not pinpoint when infection occurred or how severe it was.

Dr. Klaus Stohr, WHO's chief SARS virologist who is coordinating global research on the virus, said the study participants could not recall becoming ill, which indicates that, at most, they had mild infections.

That finding provides more evidence that there are some people who can become infected with the virus and not develop severe symptoms. Previous studies on people from the Amoy Gardens apartment complex in Hong Kong, where more than 300 people caught SARS, provided the first clue that the virus can cause a milder form of the illness.

'Not a big surprise'

"We knew that in humans there was a wider spectrum of disease, so it's not a big surprise to find this now in other humans," Stohr said. "However, these are now people who have been exposed to animals which are excreting the virus, so that indicates there is something going on between the animals and the humans."

In Singapore, animal lovers scurried to save stray cats being killed in a government cleanliness campaign aimed at combatting SARS. Animal Lovers League said its members were sending the rescued animals to a shelter in neighboring Malaysia.

He Jianfan, director of microbiology at the Shenzhen Disease Prevention and Control Center, said he believes the results indicate the workers caught the virus from the animals, developed a mild form of the disease, but then the virus mutated into a more virulent form before it was passed on to other humans.

"We have an end point and a beginning, but what's happening in between? We don't know," Stohr said. "I believe that this is one of the more likely hypotheses that would fit into the pattern of what we have seen with other diseases."

The idea that the animals could have gotten the virus from humans cannot be ruled out, Stohr said, but the findings add another piece to the puzzle and further support the theory that it jumped from animals to humans.

"Now knowing that the humans have also (developed antibodies), it would make it a bit more likely that really the animals are giving it to the humans," he said.

"The data are incomplete but there appears to be a link between the severity of the disease and the duration and amount of virus excretion in the humans," Stohr said, adding that the people who developed antibodies and a mild form of the disease may not shed enough virus to spread it.