The bird flu virus that can kill humans has the potential to be spread by cats, scientists have found.
Many chickens have been culled
It had been thought that domestic cats were resistant to diseases caused by influenza A viruses - one of which, H5N1, is responsible for avian flu.
The disease killed at least 20 people in Asia earlier this year, and forced farmers to cull almost 200m birds.
The research, by Erasmus Medical Center, Rotterdam, is published in the journal Science.
The researchers warn that their findings may mean that cats are a potential source of infection for humans.
It also underlines the ability of the virus to evolve to infect new species.
H5N1 cannot currently pass from person to person, but scientists fear that if the virus does acquire this ability, it could pose a serious threat to millions.
The Dutch team focused on cats after some anecdotal reports emerged during the recent outbreak linking the disease to the animals.
They investigated whether the virus could make cats sick when it was introduced into the airways, or when the cats ate infected chickens.
The six cats developed severe lung disease and passed the disease onto two additional cats kept in close quarters.
The authors also tested the effect of another type of influenza virus, H3N2, that most commonly causes flu in humans.
Cats exposed in the same way to this virus did not develop disease.
Writing in Science, the researchers say: "The implications are that, during H5N1 virus outbreaks, domestic cats are at risk of disease or death from H5N1 virus infection, either due to feeding on infected poultry or wild birds, or due to contact with infected cats.
"Second, the role of cats in the spread of H5N1 virus between poultry farms, and from poultry to humans needs to be re-assessed.
"Third, cats may form an opportunity for this avian virus to adapt to mammals, thereby increasing the risk of a human influenza pandemic."
Professor John Oxford, an expert in virology at Queen Mary College, London, told BBC News Online the study was "very significant and slightly alarming".
He said there was little evidence at present that cats could be infected with other forms of human flu virus, and so the possibility that H5N1 could mix with a human virus inside a cat and produce a deadly new strain was probably slim.
However, he agreed that it was possible that cats could be responsible for avian flu spreading from farm to farm - a phenomenon which has baffled scientists.
Professor Oxford said there was also work to suggest that pigs could be infected with H5N1, and, unlike cats, they could also harbour human versions of the virus.
"H5N1 is getting more and more worrisome," he said.
"If any virus is going to cause a great human pandemic in the near future, then it is likely to be H5N1."