Lab-Altered H5N1 Flu More Infectious to Humans than Birds

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.

April 26, 2013

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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