The bird flu strain found in┬аcows in the United States is not easily transmitted through the┬аair among ferrets, a new study shows, although the scientist who┬аled the work said it had shown some ability to spread this way.
Ferrets are considered to be the best small mammal for┬аstudying influenza virus infection and transmission┬аand are┬аoften used to inform assessments of the public health risk of┬аemerging viruses.
In the experiment led by researchers at the University of┬аWisconsin-Madison, ferrets infected with a sample of the H5N1┬аbird flu strain were placed near healthy animals, but not close┬аenough for physical contact.
None of the four healthy ferrets exposed in this way became┬аill, and no virus was recovered from them during the study.
However, one of the ferrets had produced antibodies to the┬аvirus, the researchers later found, suggesting it had been┬аinfected.
“It is good news that the virus does not have extensive┬аtransmissibility between ferrets through the air, but it is┬аconcerning that it has the ability to transmit [at all in this┬аway],” 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 between┬аhumans would pose a greater pandemic threat than H5N1 currently┬аdoes.
That risk is currently assessed by public health agencies┬аworldwide as low, as there is no evidence yet of any┬аhuman-to-human transmission.
Four human cases have been reported in the U.S. since avian┬аflu was confirmed in dairy cows in March. All have recovered.
The study, published on Monday in Nature, also showed the┬аbird flu virus in cows can bind to human-type receptors under┬аlab conditions. These receptors are how flu viruses typically┬аenter and infect human cells in the real world.
Bird flu prefers to bind to avian-type receptors only, which┬аare scarce in humans. The lab results need further study┬аto┬аassess their real-world implications, scientists said, as in the past flu viruses that developed the ability to bind to both┬аtypes have caused human pandemics.
The study also confirmed that the virus, isolated from the┬аmilk of an infected cow in New Mexico, made both mice and┬аferrets sick after exposure to the unpasteurized milk.
A look at CBC News coverage of H5N1тАЩs spread across the globe between 2004 and 2024, from early bird flu outbreaks in Asia to the ongoing spread of the virus in dairy cows.
It also spread through the body to muscles and mammary┬аglands in infected mice, as it appears to do in cows.
Angela Rasmussen, a virologist at the University of┬аSaskatchewan, said it was a relief to see the virus┬аhad not yet acquired the capability to cause a human pandemic,┬аbut this did not mean it would never do so, particularly if the┬аspread among cows goes unchecked.
“It’s always better to stop a pandemic before it starts than┬аto respond to it once it has started. We should heed this┬аwarning and take action now,” she said via email.┬а
