for National Geographic News
The source of SARS has mystified medical experts. Some believe it evolved naturally in humans. Others say it must have jumped from an animal, maybe a chicken or an exotic bird. But one group of British scientists suggests a more far-out origin: space.
In a letter to the British medical journal The Lancet, Chandra Wickramasinghe, from Cardiff University in Wales, and other scientists, propose that SARS may have originated in outer space then fallen down to Earth and landed in China, where the outbreak began.
It sounds like a headline from a supermarket tabloid, but the idea may not be as outlandish as it first appears. One hundred tons (90 metric tons) of space debris fall on Earth every day; some scientists believe as much as one ton (0.9 metric ton) of bacteria from space is part of that daily deposit.
Particles carrying the SARS virus could have come from a comet, the researchers say, and released into the debris trail of the comet's tail. The Earth's passage through the stream would have led to the entry of the culprit particles.
"We're not saying this is definitely what happened," said Wickramasinghe, who is also the director of the Cardiff Centre for Astrobiology, a research effort that seeks evidence of extraterrestrial life. "But the theory should not be ruled out."
SARS, or severe acute respiratory syndrome, has so far infected at least 8,384 people and claimed 770 lives. Mainland China, Hong Kong, Taiwan, and Canada have been hit hardest by the epidemic.
Although SARS has been identified as a coronavirus, the virus is unexpectedly novel. An independent evolution of the virus may have been required, which, Wickramasinghe says, adds credibility to his argument that SARS has an external origin.
According to his theory, a small amount of the virus introduced into the stratosphere could have lead to an initial fallout east of the Himalayas, where the stratosphere is thinnest, followed by sporadic deposits in neighboring areas.
"There would be a first point of descent," said Wickramasinghe. "This could have been in China."
But most medical experts are sticking to a more conventional explanation for the origin of SARS.
"We have no scientific evidence that SARS or any other infectious disease has dropped off a meteor at this point in time," Julie Gerberding, director of the Atlanta-based Centers for Disease Control and Prevention, said at a recent briefing. "Should we discover any evidence supportive of that, we would let you know.
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