Or that the virus jumped to humans from other animals, such as rats and mice that are consumed by the wild animals sold in markets.

WHO expert Francois Meslin, responding to new evidence that found the Sars virus in three small mammals,including a civet cat that is eaten as a delicacy by some, said: 'It's certainly too early to draw final conclusions on those findings but they are clearly quite exciting.'

Researchers from the University of Hong Kong examined 25 animals representing eight species in a live animal market in southern China that supplies restaurants in Guangdong province, where the Sars outbreak is said to have started.

Six of the animals tested were masked palm civets, which look like long-nosed cats but are related to the mongoose. All the civets, which came from several different owners at the market and appeared healthy, tested positive for a Sars-like virus, said WHO's chief Sars virologist Klaus Stohr.

One raccoon dog, which is a member of the dog family native to eastern Asia, was investigated and found to have the virus in its faeces. Antibodies against the virus were found in the dog.

Antibodies were also found in the one badger that was examined, Dr Stohr said.

But the results from the civets were considered the strongest because the virus could be isolated from their bodies, they carried antibodies and they all tested positive despite belonging to different owners and being kept on different sides of the market.

'That's a relatively strong indication that these animals may play a particular role,' Dr Stohr said.

However, the market study could not tell whether the civets are a species that maintains the Sars virus in nature. Such animals are known as reservoirs.

It is possible that they play some other role in a chain of transmission from animals to humans, said Dr Meslin, who coordinates a WHO team in Geneva that deals with diseases that can jump from animals to humans.

Some viruses that have jumped from animals to humans involved multiple animals playing different roles.

While one species may be the reservoir, others can be what are known as 'amplification hosts', whereby they are infected by the reservoir species and then pass on the bug to humans.

'We cannot say those animals are the source of the initial cases of Sars,' Dr Meslin said.

'We really need to investigate more the relationship between the different animal species found to have the virus, and maybe others.

'These animals can consume small mammals, particularly rats and mice, and those could be the source of the infection, so for the time being, it's all conjecture,' he said.

Dr Stohr said it was possible that the animals could have all become infected through feed given to them at the market, or they could have infected one another.

It was also theoretically possible that the animals at the market contracted Sars from humans, perhaps by a sick person coughing into the cages, he said. -- AP