Ferrets closely mimic human symptoms of SARS. Credit: © GettyImages

A new study has heightened fears that severe acute respiratory syndrome (SARS) could hit back this winter. The pool of animals harbouring the lethal virus may be bigger than first realized, researchers warn.

SARS is thought to have jumped to humans in the live-animal marketplaces of Guangdong, China, last year. It raced round the world, claiming more than 770 lives, before public-health officials stamped it out.

Now teams in the Netherlands and Hong Kong have found that the SARS virus, which is a new type of coronavirus, infects domestic cats and ferrets, even though the two species are distantly related. It also scuttles into healthy animals from sick ones1.

The SARS virus' promiscuity implies that it may be lurking in a menagerie of wild or domestic animals - and might readily jump into humans again. It will also make the source of an outbreak more difficult to track and contain. "It could be much, much harder than we thought," says Dick Thompson, a communications officer with the World Health Organization (WHO) in Geneva, Switzerland.

The study lengthens the list of animals that carry the SARS virus - it includes masked palm civets, raccoon dogs and ferret badgers from a Guangdong market. Cats in the Amoy Gardens apartment block in Hong Kong, where a rash of residents caught SARS, were also infected.

Red alert

Worldwide hospitals and laboratories are on red alert for a whiff of SARS. "We have to be prepared for this virus to strike back," says Albert Osterhaus of Erasmus Medical Centre in Rotterdam, who led the latest study.

Many experts predict that the virus, like those that cause some colds and influenza, might rear up again as winter approaches in the Northern Hemisphere.

SARS could materialize by several routes: a second leap from wild animals, a jump from animals infected by humans - or an escape from one of the many labs that are growing and studying the virus. A Singapore lab worker was infected this way in September.

A cluster of patients with pneumonia-like illness should ring alarm bells, explains Thompson. He believes that countries that were previously affected will quickly squelch out SARS with tough public-health measures such as patient isolation. They know how damaging an outbreak can be, he says.

Test case

A key problem for hospitals facing a suspected SARS patient is the lack of a reliable diagnostic test. This is one of the research priorities identified by the WHO's SARS Scientific Research Advisory Committee, a panel of more than 30 researchers who met for the first time last week.

Only if the third level comes back positive would we consider we have a case of SARS Dick Thompson, , WHO

To avoid crying wolf, the experts recommended that suspected SARS patients be tested at least three times: with two different tests and then again by an external lab. "Only if the third level comes back positive would we consider we have a case of SARS," says Thompson.

Should a case be diagnosed, doctors still have little in the medicine cabinet. Researchers hope that the infected ferrets, which mimic the symptoms of the human lung disease, should prove better for testing drugs and vaccines than the monkeys that have been available so far. "It's much, much easier now," says coronavirus researcher Peter Rottier of the University of Utrecht in the Netherlands.