Sars researchers discover more questions than answers

WASHINGTON - They have the latest gene-sequencing equipment, million-dollar biosafety labs and satellite linkups to compare notes.

But the international team of scientists trying to understand Sars are hampered by the uncertainties of biology.

In less than a month, two labs sequenced the entire genome of the virus suspected of causing Sars - a first step to finding out where it came from and what the best approach might be for formulating drugs and vaccines.

But even as Dr Julie Gerberding, director of the US Centres for Disease Control and Prevention, called the accomplishment unprecedented, she acknowledged that it would lead to no quick breakthrough.

"In the short run I don't think the sequence data alone is going to tell us where it came from.

"We need to go back to the first cases of Sars in Guangdong and do shoe-leather work to find out who the people were, what life they were leading, who they were in contact with."

To find out if the virus jumped from animals to people, investigators need to determine what animals the first victims came into contact with.

Sars has been consistent in some ways. It makes patients very ill only if they develop pneumonia, and worldwide kills 4 per cent of patients.

Like other respiratory viruses, it seems to spread in large droplets, like those people produce when they cough, sneeze or talk. Like cold and flu viruses, it may also be spread on objects such as lift buttons.

What is not known is why some people seem more infectious. Such super-spreaders include a 26-year-old Hong Kong man who directly infected 112 people - 69 of them hospital workers who had cared for him - and a further 26 indirectly.

Perhaps some patients sneeze more, or have more virus in their nasal passages, or are infected with a more virulent strain.

"It just tells us the virus has a highly variable nature. We wish we knew why," Dr Gerberding said.

Infectious disease experts are used to such inconsistencies. Viruses and bacteria swap genes, they mutate, they evolve - all at high speed.

The suspect virus in Sars, a coronavirus, is prone to the kinds of "mistakes" that can make it mutate. Like the Aids virus, it uses RNA and not DNA to replicate itself.

Scientists also want to know if people with Sars can infect others even before they become ill themselves, which is vital in terms of controlling the epidemic. It is easy to isolate people who show symptoms such as coughing and a fever, but those who appear healthy can infect many around them.

Some of the tests being used to diagnose the virus in patients in China seem to have found it in people who do not have symptoms.

Searching for Sars

* Scientists say knowing the genetic sequence of the virus is probably not enough.

* To find a cure, they need to know how it crossed from animals to people.

* Only detailed knowledge of patients' lives will supply these answers.

* "We need to go back to the first cases of Sars in Guangdong and do shoe-leather work to find out who the people were, what life they were leading."

- Dr Julie Gerberding, director of the US Centres for Disease Control and Prevention

- REUTERS