CBC In Depth
Hunting Down SARS
Reporter: Kelly Crowe | May 28, 2003

They know what it looks like, and they know the damage it can do, but to solve the mystery of SARS, scientists need to know where the deadly new coronavirus came from. Now they've found a clue, in the wild animal markets in the heart of China's SARS-ridden Guangdong province.

Laurie Garrett is an award-winning science writer, author of The Coming Plague. Emerging viruses are her specialty. As soon as SARS erupted, she went to China to cover the outbreak. She found herself in the market where she found cage after cage of exotic animals: bamboo rats, barking deer, hog-nosed badgers, even domestic cats, dozens of species stacked together, all of them for sale, all destined as delicacies for the dinner table.

"This market was seated right in the centre of Guangzhou and fills about a full city block. There are markets like it all across that province with every imaginable kind of animal crunched up in those cages. The cages [are] simply stacked one atop another atop another, and with humans running all around in the middle of it all," Garrett says.

"Most individuals do not personally buy and take them to their home kitchen, except on very special holidays. So the bulk of the purchasing is actually from large restaurants and hotels that serve elite clientele."

It's restaurant food handlers and chefs who do the killing and the cooking. It seems they were also getting SARS. More than 30 per cent of the Guangdong victims had some connection to the food trade. That led investigators to the markets, where they took samples from more than 25 animals of different species and tested them. On the very first try, they found what they were looking for.

"In the past month, we have been able to do a lot of work on sampling the fecal material of the wild animals, and from a special type of civet, civet cat, we are able to isolate the coronavirus. And this coronavirus on genomic analysis was found to be very, very similar to the coronavirus causing SARS in humans," Dr. Yuen Kow-yung of the University of Hong Kong told reporters.

The scientists found the SARS coronavirus in six Himalayan civets. The researchers also found the virus in another species, a raccoon dog, and they found antibodies in a badger. It's early confirmation of something they've always believed: that SARS jumped from animals to humans.

Dr. C. J. Peters is the former head of special pathogens at the U.S. Centers For Disease Control and Prevention. He's also an expert in tropical diseases. He says the question now is this: did SARS make a simple leap from civets straight to humans, or did the virus travel through some other species first?

"It gives us a prime suspect and it gives us a context in which we can work and try to pin this down more carefully. I think it's a very important finding, and I think the scientists who came up with this are to be congratulated on their initiative and their skill," Peters says.

"Situations in nature are often sort of tricky and complicated," he adds. "We know that this virus was isolated from more than one civet cat according to the report, but we don't know whether the civet cat actually gave it to something else that gave it to humans or whether there's some third animal out there that gave it to humans and the civet cat. There are a lot of possibilities, but we are a whole lot closer."

It's not the first time a virus has made the deadly jump from animals to humans. Before Ebola started killing people in Africa, scientists believe it lived in animals. They still don't know which one. There was the deadly Nepa virus that swept Malaysia in 1998. It hopped from wild bats to pigs to humans, eventually killing 100 people. Every year, the world battles a new flu virus, courtesy of the ducks and pigs kept outside many rural homes in China.

"We now know that influenza is actually an aquatic migratory bird virus," Garrett says. "So what you have happening is aquatic birds flying over these tethered [domestic] ducks and the bird droppings infect the tethered duck. The tethered duck then spreads its virus to the pig and then the farmers become infected from exposure to an ailing pig. That's why every year, the new mutant strains of influenza always come back to China."

Now scientists are close to proving that the SARS virus made that same dangerous journey from animals to humans, possibly in the cages of the Guangdong market.

"I think the markets were a very logical place to look because that is one place where animals and humans came together, and intimately. Furthermore, the animals were held in cages and under stress; in certain other circumstances, some coronaviruses are activated by stress. Some of the animals at this market did look stressed and some literally sick," Dr. Peters says.

But the markets have been around for generations while SARS is a brand new virus – possibly just over six months old – so scientists must determine what went wrong to tip the biological balance and spark a deadly new disease.

Although the scientists say it's too early to draw any final conclusions, Chinese officials seem to have made up their minds: they're showing a sudden interest in protecting endangered animals, the same species that have been sold in the marketplace for decades. Meanwhile, thousands of markets, restaurants and kitchens throughout Guangdong have been raided, shut down and hosed clean in a desperate attempt to wash away the latest intruder from the microbial world.



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