News / Health

Lab-Altered H5N1 Flu More Infectious to Humans than Birds

A staff member works on a blood sample of a chicken at the Veterinary Research Bureau.
A staff member works on a blood sample of a chicken at the Veterinary Research Bureau.
Jessica Berman
A new study suggests a laboratory-mutated H5N1 avian influenza virus could pose a greater risk to humans than to birds, adding to concerns about the new avian flu strain that has emerged recently in China. 

Over a year ago, Japanese researchers created a genetically-altered version of the H5N1 avian influenza virus to explore the risk of human-to-human transmission. They reported in the journal Nature in early 2012 that the mutated pathogen could be transmitted among mammals through the air in aerosol droplets -- for example, from sneezing. They conducted their experiments with ferrets, small domesticated mammals that are a good model for human disease transmission.

The experiment showed that the viral strain has the potential to cause a global human pandemic, even without contact with infected poultry or even person-to-person contact. That finding sparked international security concerns that the pathogen could be used as a biological weapon.  

So far, 600 cases of H5N1 in humans have been reported to the World Health Organization.  The virus causes severe pneumonia and respiratory failure.  The illness has killed 60 percent of those who have contracted it.  

Following up on the Japanese research, an international team studied just how infectious the virus would be to humans, should mutated copies ever jump the species barrier.  

John Skehel is a virologist with the National Institute for Medical Research in London. Writing in the journal Nature, Skehel and co-researchers describe how effectively amino acids from the mutant bird-flu strain are able to bind, or latch onto human cell surface proteins or receptors, as compared with bird or avian cells.

“And we find that it will bind to human receptors about 200 times better than it binds to avian receptors,” Skehel explained.

In other words, humans appear to be at far greater risk than birds of becoming ill with the deadly mutated form of the H5N1 virus.  And even though the mutant virus' grip on human cells is not as strong as that of other infectious flu viruses, it still appears, in the laboratory, to be highly contagious to human cells  -- a finding one researcher described as "confounding."

As scientists continue to learn more about H5N1, international public health officials are also keeping a close watch on another avian flu virus, which the World Health organization is calling one of the most lethal pathogens doctors have ever faced.

Since it was detected this past February, the H7N9 influenza strain has infected more than one hundred people in China, mostly in Shanghai, and killed nearly one-quarter of them.  So far, all human cases appear to have resulted from contact with infected birds, and the new strain has shown no signs of being transmissible from human to human.

Tom Frieden is director of the US Centers for Disease Control and Prevention, or CDC, headquartered in Atlanta, Georgia.

Frieden says H5N1 -- in its natural, unmutated form -- is easy to spot and control because infected flocks become visibly sick.  Not so with H7N9.

“With H5[N1], the birds get sick and the country culls the flock and it stops spreading.  Here, the birds don’t get sick so you can’t cull the flock,” stated Frieden.

Frieden says the CDC, like a number of other international medical research centers, is studying samples of the H7N9 virus it acquired from China. The CDC is working closely with Chinese health officials to develop a vaccine against the new bird flu.

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