Portrait of a probable killer

Viral double act implicated in 'killer flu' epidemic.
28 March 2003

HELEN PEARSON

Coronaviruses cause about one in three colds. © SPL

If scientists' hunch proves correct, the mystery 'killer flu' that has killed more than 50 people in Asia and beyond is an infection like none seen before.

Suspicions are growing that the culprit is an unassuming virus called a coronavirus. Many labs have found a version of it in most patients' lungs and blood; some sufferers also have antibodies that show they were infected.

But the coronavirus might have a partner in crime: a virus that was discovered last week. This pathogen, one of the paramyxoviruses that cause respiratory infections, has also turned up in some swabs. "It could well be that a combination is important," says virologist Albert Osterhaus of Erasmus University Hospital in Rotterdam, the Netherlands.

The coronavirus may weaken patients' immune defences, leaving them vulnerable to the second bug. Alternatively, it could be acting alone, and the presence of the paramyxovirus - which is common in winter months - may be a fluke.

Either way, there is little in the pharmacy to fight a coronavirus, says Robert Sidwell, who directs the Institute for Antiviral Research at Utah State University in Logan. "It's not been a high-priority virus," he says.

The US Department of Defense is already screening anti-viral medicines against the suspect coronavirus to find one that curbs its growth. Some clinics have tried a common drug called ribavirin, but are unclear whether patients are recovering better than those who go without.

Meanwhile, most affected countries are containing the disease by isolating patients. There are fears that this process is not watertight in Hong Kong and China, where the worldwide outbreak is thought to have started.

Shuffling on

Health officials' concern over the mystery disease - known as severe acute respiratory syndrome (SARS) - is heightening by the day. The global tally of probable cases leapt from nearly 500 to 1,323 this week, largely because Chinese health authorities officially increased their count.

"If SARS is a coronavirus, it'll be one of the most severe ever reported," says Michael Lai, who studies the pathogen at the University of Southern California in Los Angeles. The viruses cause around a third of common colds - but have rarely killed.

But coronaviruses are prone to transformation. They have an unusually large amount of genetic material, as well as enzymes that enable them to shuffle it. A new, more virulent mutant could easily result.

The virus might also be a strain that only recently made the jump into humans from animals. Investigators are trying to work out whether the bug has an animal counterpart by reading its genetic sequence.