Pet theory comes to the fore in fight against SARS.

The domestic cat is set to land a starring role in the future course of severe acute respiratory syndrome (SARS) — although it isn't yet clear whether it will be as saviour or scourge.

Experts have identified the cat as a potential animal model for SARS, but it may also fit the bill as a reservoir species for the SARS virus, guilty of bringing humans into contact with the disease.

Late last month, Chinese scientists revealed that several species of wild animal on sale in the markets of southern China were harbouring a virus very similar to that believed to cause SARS (see 10.1038/423467a). It is unclear whether these animals are a reservoir for the virus, or were infected by another species. And experts are now wondering whether a domestic animal may also be a reservoir species.

The only animal model available for SARS is the macaque monkey, which is expensive to use. Attempts to infect mice with the SARS virus have so far failed. But some pet cats in the Amoy Gardens apartment block in Hong Kong, where more than 100 residents contracted SARS in April (see 10.1038/423003a), were found to harbour the virus, and to get sick from it.

“The cat may offer an alternative,” says Albert Osterhaus, a virologist at Erasmus University in Rotterdam who developed the macaque model. Osterhaus has applied for ethical authorization to begin systematic studies on cats. Other laboratories, including the US Centers for Disease Control and Prevention in Atlanta, Georgia, are also assessing the cat's potential as an animal model.

If cats prove to be susceptible to infection, they could be responsible for bringing SARS into homes. The World Health Organization (WHO) is keen to define all possible reservoirs among species that come into regular direct contact with humans. It is establishing an international network of laboratories with expertise in zoonotic diseases — infections that jump between species — to address the problem.

Researchers at the National Microbiology Laboratory in Winnipeg, Canada, have already tested pigs and chickens and have found no evidence that they can be infected by the virus.

“We want to recruit more specialized labs around the world to help extend this type of work to all domestic species,” says Klaus Stöhr, the WHO's chief SARS expert, based at the organization's Geneva headquarters. He warns that a domestic animal acting as a reservoir would pose a greater risk to humans than if only wild species harbour the virus.