What Causes SARS? Hints, but Still No Firm Answers

Scientists scrambling to pin down the cause of the frightening respiratory illness spreading worldwide are nearing an answer, but as of Thursday the picture remains decidedly uncertain.

Scientists scrambling to pin down the cause of the frightening respiratory illness spreading worldwide are nearing an answer, but as of Thursday the picture remains decidedly uncertain.The prime suspect is a coronavirus that probably originated in animals, said World Health Organization (WHO) expert Dr. Wolfgang Preiser, but current theories about severe acute respiratory syndrome (SARS) hint that another recently discovered virus and even a new form of chlamydia might also play a role in some patients. “It’s a very varied picture, and it may already be outdated in two days’ time because the evidence is rapidly evolving,” Preiser told Reuters Health in a telephone interview. The German researcher is one of five experts on a WHO mission to learn more about SARS at the epicenter for the disease in China’s southern Guangdong province. His laboratory in Frankfurt was involved in treating three patients in Germany. One day after they arrived in Guangdong, the WHO group has confirmed that the outbreak of “atypical pneumonia” reported by Chinese authorities last year is the same thing as SARS. But other crucial questions, like what causes the disease and where it came from, are unanswered. CERTAINLY SOMETHING NEW The first step for the WHO network of laboratories was to rule out known infectious agents as the cause of SARS. That has now been ascertained, thanks to a molecular technique called polymerase chain reaction (PCR), which can detect tiny pieces of genetic material. “We are quite certain that we were dealing with a new agent,” Preiser said. “This is something that has not been described before in humans or animals.” The collaborators then set about trying to grow the agent in the laboratory. Several labs around the world identified coronavirus in their local patients, and a comparison showed they were highly genetically related. “They are virtually indistinguishable,” Preiser said. Coronaviruses can cause the common cold in humans, and serious diseases in animals. The evidence hints that the new virus has jumped from an animal, but Preiser said facts were not strong enough yet to say what kind of animal. WHY DO SOME DIE, SOME SURVIVE? In some patients, SARS spreads extremely aggressively and causes severe disease — killing about 3.5 percent of those infected. But others recover quickly and do not seem to have infected many other people. “We don’t know why that should be,” Preiser said. “It’s obvious that they’ve been exposed to the same agent.” Two other findings could, just possibly, explain this. First was the identification by German and Canadian researchers of another virus in some patients with SARS. The metapneumovirus — part of the paramyxovirus family — was discovered only recently, but is known to cause respiratory diseases in children. “Human metapneumovirus may play an important role as a co-factor, because it is quite unexplained so far why some patients spread the illness to many others, and some patients don’t seem to spread very much — also, why some patients fare very badly clinically, and others have a rather mild disease,” Preiser said. The same could be true for chlamydia, a common type of bacteria that can cause respiratory infections. In several patients, doctors have found evidence of infection with a chlamydia species. “This may be one of the chlamydia species that we know already, or it may, alternatively, be something new,” Preiser said. In the end, however, all this might be overturned as new evidence arises. Scientists in the WHO network are talking on a daily conference call and posting information on a secure Web site. “All types of things have to be done still,” the German researcher said, including wide-ranging tests to see how common the new coronavirus is in the general population and a crucial experiment to see if it will trigger disease in animals. “That is actually going on at the moment,” he said.(Source: Reuters)