Study tracks SARS' jump from animals to humans
SARS was an animal disease that jumped the "species barrier" to humans, says a group of Chinese scientists who have identified three stages in the evolution of the disease that turned it into a deadly human infection.
The researchers, working with a team at the University of Chicago, analyzed more than 60 SARS viruses and found that it took only three major changes to the virus' genetic material for it to stabilize and spread easily among humans.
During the first phase, the SARS virus was virtually identical to that found in wild animals and infected only 3 percent of the people who came in contact with it, according to the study published in the journal Science. It mutated to cause a second phase, however, and spread from human to human. After further mutations, a third phase allowed the disease to spread even more easily among humans, infecting about 70 percent of those who came in contact with it.
"What we see is the virus fine-tuning itself to enhance its access to a new host — humans. The virus improves itself under selective pressure, learning to spread from person to person, then sticking with the version that is most effective," said Chung-I Wu, a professor at the University of Chicago.
While the study confirmed that SARS originated in animals, it did not determine which animal was the natural "reservoir" for the virus (Steve Connor, London Independent, Jan. 30).
The Ministry of Health in China, where SARS first broke out, said yesterday that no new cases of the disease had been reported there in the past 24 hours. It also said that all three diagnosed SARS cases this winter had recovered and been discharged from the hospital (Xinhua News Agency/People's Daily, Jan. 29).