Bird flu virus in US cow outbreak does not spread easily through the air, ferret study shows

A new study shows that the bird flu strain found in cows in the United States is not easily transmitted to ferrets through the air. However, the scientist who led the study said the strain can still spread this way.

Ferrets are considered the best small mammals for studying influenza virus infection and transmission. They are often used to assess the public health risks of emerging viruses.

In the experiment, led by researchers at the University of Wisconsin-Madison, ferrets infected with a sample of the H5N1 bird flu strain were placed near healthy animals, but not close enough for physical contact.

None of the four healthy ferrets exposed in this way became ill and no virus was found in them during the study.

However, the researchers later discovered that one of the ferrets had produced antibodies against the virus, indicating that the ferret was infected.

“It is good news that the virus cannot be widely transmitted through the air between ferrets, but it is concerning that the virus does have the potential to infect other ferrets. [at all in this way]”, said study author and influenza virologist Yoshihiro Kawaoka.

No evidence yet of human-to-human transmission

A virus that can spread easily through the air between people would pose a greater pandemic threat than H5N1 currently poses.

Public health authorities worldwide currently consider the risk to be low, as there is no evidence yet of human-to-human transmission.

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

The study, published Monday in naturealso showed that the avian flu virus in cows can bind to human-type receptors under laboratory conditions. These receptors are how flu viruses typically enter and infect human cells in the real world.

Bird flu prefers to bind only to bird-like receptors, which are scarce in humans. The lab results need to be studied further to assess their real-world implications, scientists said, since flu viruses that evolved the ability to bind to both types have caused human pandemics in the past.

The study also found that the virus, which was isolated from the milk of an infected cow in New Mexico, sickened both mice and ferrets after exposure to the unpasteurized milk.

WATCH | Headlines from the two-decade bird flu pandemic:

20 years of bird flu in the news and cause for concern about pandemic

A look at CBC News’ coverage of the global spread of H5N1 between 2004 and 2024, from early outbreaks of bird flu in Asia to the continued spread of the virus among dairy cows.

In infected mice, the disease also spread through the body to the muscles and mammary glands, just as it appears to do in cows.

Angela Rasmussen, a virologist at the University of Saskatchewan, said it was a relief that the virus had not yet reached the point of causing a pandemic in humans. But that didn’t mean it never would, especially if the spread among cows remained unchecked.

“It is always better to stop a pandemic before it starts than to react to it once it has started. We must heed this warning and take action now,” she said via email.

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