Mammals from China market may be source of human infection
By Rob Stein
THE
WASHINGTON POST
http://www.msnbc.com/news/917760.asp?0dm=N224H
May 24 — Scientists have discovered the first clue to the origins of the SARS virus, identifying a virtually identical microbe in two small mammals, and possibly a third, that are eaten as delicacies in China.
THE FINDINGS, announced yesterday, prompted Chinese officials to ban the sale of the animals to try to stem the spread of the disease and prevent new outbreaks, World Health Organization officials said.
While determining the exact role of the animals in the epidemic must await further research, the findings could be a crucial development in the battle against severe acute respiratory syndrome, which has stricken at least 8,117 people and killed at least 689 worldwide.
Discovering the source of the virus would be critical for determining how the infection arose. It could also allow health authorities to eradicate reservoirs in nature where the virus could hide, and from there reemerge, if the human infections are wiped out. That could allow the illness to be eradicated.
“We believe the window is still open to eradicate this disease,” said Klaus Stohr, WHO’s top SARS scientist. “It is wider now that we may have pinpointed the animal reservoir.”
ANIMAL LINK FOUND
Since SARS emerged in November, scientists have speculated that the disease may have originated when a previously unknown virus mutated in a way that allowed it to jump from an animal to humans. That is often how new human illnesses develop. The AIDS virus, for example, may have jumped to humans when a monkey virus mutated and infected someone butchering an animal for meat. But the SARS virus was unlike any known related viruses, and an intensive investigation into the early cases produced no clear leads, despite reports that at least some of the early victims were chefs.
The long-sought discovery came when a team of researchers from the University of Hong Kong and the Chinese government tested 25 animals from eight species being sold at a live animal market in the province of Guangdong, where the disease first emerged.
The tests found a virus that appeared
virtually identical to the SARS virus in saliva and feces of six catlike
animals, known as masked palm civets. The researchers directly isolated virus
from four of the animals and found pieces of genetic material from the microbe
in two others. Tests also showed genetic evidence of the virus in feces of
another animal, known as a raccoon dog, and an eighth animal, a Chinese ferret
badger, had antibodies to the virus in its blood. None of the animals was sick.
MISSING PEPTIDE
A detailed genetic analysis of the virus isolated from the animals found it was identical to the SARS virus from human patients except that it lacked one sequence. The missing genetic material carries instructions for the production of a small protein, known as a peptide, and may have been the change that allowed the virus to jump to humans and then spread readily, Stohr said.
“The lack of this peptide may have helped the virus transmit efficiently from human to human,” Stohr said. “Perhaps that missing piece of protein is just the trick, the little difference between a harmless animal virus and a human pathogen. That’s a bit of speculation, but this is one hypothesis.”
The civets appear to be the most likely candidates, since the virus was found in more of those animals than any other. In addition, China apparently began importing the animals in significant numbers from Vietnam within the past year, Stohr said.
“That would fit with the occurrence of this disease,” Stohr said.
Civets are nocturnal creatures related to the mongoose. With long tails and catlike bodies, they resemble small raccoons or weasels and have become prized by chefs at pricey restaurants.
There are many unanswered questions, Stohr said. It is unknown whether the animals were trapped in the wild or bred on farms. It is also unknown whether the animals came to the market infected or became infected on arrival. The animals analyzed represented a sampling from different parts of the market, though, which is evidence they did not necessarily infect one another.
PUBLIC HEALTH RISK
“What these findings mean is that the SARS coronavirus exists outside humans,” Stohr said. “It’s being excreted in certain amounts in animal species. That means there’s a public health risk and that someone dealing with these animals or handling them could become infected.”
If the animals are spreading the virus, it is more likely occurring when they are handled or slaughtered, and not when they are eaten, because cooking would kill the virus, Stohr said. The animals are not believed to be commonly eaten raw.
“If this virus is as widespread as this small-scale study would suggest, it would suggest that the public health risk is not localized, but that it’s practically everywhere,” he added. “We know these animal markets exist in many places in China.”
“Until the role of this animal species is verified, all those who might come in contact with these animal species should be aware of the possible health risks,” Stohr said.
He cautioned, however, that no one knows how much virus is excreted by the animals and how much is necessary to cause infection. It may also turn out that the animals contracted the virus from feed or perhaps yet another, unidentified species that is the true reservoir.
“We cannot rule out the possibility that these animals were all infected by a SARS patient who was going around and coughing into cages,” Stohr said. “It’s unlikely, but we can’t rule it out.”
Tests of three hog badgers, three beavers, two Chinese muntjacs, four Chinese hares and four domestic cats at the market were negative, Stohr said.
© 2003 The Washington Post Company
