Chinese scientists compared the genetic makeup of viral particles isolated from humans with SARS with a virus found in wild animals recently captured and being held in a retail food market.
The animals were found to have a corona virus that was 99.8 percent genetically identical to a virus that causes severe acute respiratory syndrome, or SARS, in humans.
Their findings suggest that the markets provide a venue for the animal (corona virus) viruses to amplify and transmit to new hosts, including humans and this is critically important from the point of view of public health.
The researchers found the virus in civets, raccoon-dogs and ferret badgers that were offered for sale as food in a market in Shenzhen, but said it is not clear if these animals were the natural source of the virus.
"It is conceivable that (the market animals) were all infected from another, as yet unknown animal source which is in fact the true reservoir in nature," the researchers said.
They also tested merchants in the market and found that eight of 20 wild animal traders and three of 15 workers who slaughter the animals had antibodies to the virus. Only 5 percent of the vegetable traders in the same market had the viral antibodies. None of those tested, however, reported symptoms of SARS in the past six months.
Ban on some animals lifted
The study was conducted by 18 researchers from the University of Hong Kong, and from two government health agencies.
SARS was first recognized in the Guangdong Province in China in November. It spread to Hong Kong in February and eventually to more than 30 other countries. More than 7,900 people worldwide developed SARS and more than 800 died.
The disease subsided in June, but health experts fear it could re-emerge this fall as the weather turns colder.
A SARS infection can cause flu-like symptoms, including a high fever and head and body aches. Some patients develop congestion and have trouble breathing. It is spread through person-to-person contact and by inhaling droplets from coughs and sneezes of people who are infected. Severe cases can be deadly, particularly for the elderly and very young.
Researchers early on suspected that the virus was spread to humans from wild animals captured and sold for food. Chinese officials for a time banned the sale of civet cats, but that ban was lifted last month.
Henry Niman, a Harvard University professor and SARS researcher, said the new study is important because it moves researchers closer to finding the original source of the virus.
He said the study also suggests that Chinese officials should not allow selling of civet cats and similar animals for food without first checking them for the presence of the coronavirus.