The avian influenza virus that has spread widely among poultry and other birds in Southeast Asia and infected some people there has also crossed another species barrier to infect cats, and can be spread among them as well, Dutch scientists have found.
The finding is "extraordinary because domestic cats are generally considered to be resistant to disease from influenza A virus infection," like that of the avian strain, the researchers are reporting in today's issue of the journal Science.
In the Dutch study, some cats with the infection died of it, while others survived. A few did not even show any symptoms that they were carrying the disease.
Whether cats can transmit the virus strain, A(H5N1), to humans is not known. The World Health Organization has received no reports that cats played a role in afflicting the 35 people who have developed A(H5N1) infection, all in Thailand and Vietnam, said Dick Thompson, a spokesman for the agency in Geneva. Those cases were traced chiefly to direct contact with sick birds.
Even so, the Dutch study has important implications for human and animal health, said Juan Lubroth, a senior animal health officer at another United Nations agency, the Food and Agriculture Organization.
The findings, Lubroth and the study's authors said, underscore a need to investigate the possible role of cats and an array of other animals in the spread of avian influenza among poultry farms and to humans.
An estimated 200 million birds have either died of A(H5N1) or been slaughtered to control the outbreak since last winter. U.N. officials have described the scale of the epidemic - geographically and economically - as unprecedented for an avian flu outbreak.
The strain has also been particularly lethal for humans, killing 25 of the 35 people infected.
Many influenza experts and health officials fear a worst-case occurrence in which a person becomes infected with both an avian influenza virus and a human one. Under such a circumstance, the viruses might swap genes, creating a new virus that could cause an epidemic all over the planet much like that of the so-called Spanish flu of 1918-1919, which killed 675,000 people in the United States and more than 20 million around the world.
The laboratory in Rotterdam, Netherlands, that reported the new findings has conducted research on A(H5N1) since 1997, when its scientists detected the strain in a child who had died of the disease in Hong Kong.
That case was a scientific bombshell, because it was the first in which a new avian influenza virus had been transmitted from birds to humans without first mixing with mammalian influenza strains in pigs.