Bird flu strain in U.S. cow outbreak not easily spread by air, ferret study shows

The bird flu strain found incows in the United States is not easily transmitted through theair among ferrets, a new study shows, although the scientist wholed the work said it had shown some ability to spread this way.

Ferrets are considered to be the best small mammal forstudying influenza virus infection and transmissionand areoften used to inform assessments of the public health risk ofemerging viruses.

In the experiment led by researchers at the University ofWisconsin-Madison, ferrets infected with a sample of the H5N1bird flu strain were placed near healthy animals, but not closeenough for physical contact.

None of the four healthy ferrets exposed in this way becameill, and no virus was recovered from them during the study.

However, one of the ferrets had produced antibodies to thevirus, the researchers later found, suggesting it had beeninfected.

"It is good news that the virus does not have extensivetransmissibility between ferrets through the air, but it isconcerning that it has the ability to transmit [at all in thisway]," said study author and flu virologist Yoshihiro Kawaoka.

No evidence yet of human-to-human transmission

A virus that can spread easily through the air betweenhumans would pose a greater pandemic threat than H5N1 currentlydoes.

That risk is currently assessed by public health agenciesworldwide as low, as there is no evidence yet of anyhuman-to-human transmission.

Four human cases have been reported in the U.S. since avianflu was confirmed in dairy cows in March. All have recovered.

The study, published on Monday in Nature, also showed thebird flu virus in cows can bind to human-type receptors underlab conditions. These receptors are how flu viruses typicallyenter and infect human cells in the real world.

Bird flu prefers to bind to avian-type receptors only, whichare scarce in humans. The lab results need further studytoassess their real-world implications, scientists said, as in the past flu viruses that developed the ability to bind to bothtypes have caused human pandemics.

The study also confirmed that the virus, isolated from themilk of an infected cow in New Mexico, made both mice andferrets sick after exposure to the unpasteurized milk.

WATCH |Two decades of bird flu pandemic headlines:

20 years of avian flu making headlines and sparking pandemic concerns

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It also spread through the body to muscles and mammaryglands in infected mice, as it appears to do in cows.

Angela Rasmussen, a virologist at the University ofSaskatchewan, said it was a relief to see the virushad not yet acquired the capability to cause a human pandemic,but this did not mean it would never do so, particularly if thespread among cows goes unchecked.

"It's always better to stop a pandemic before it starts thanto respond to it once it has started. We should heed thiswarning and take action now," she said via email.