Genetic sequence data on a deadly strain of bird flu previously unknown in
people shows the virus has already acquired some mutations that might make it
more likely to cause a human pandemic, scientists say.
But there is no evidence so far that the H7N9 flu - now known to have
infected nine people in China, killing three - is spreading from person to
person, and there is still a chance it might peter out and never fully mutate
into a human form of flu.
Just days after authorities in China announced they had identified cases of
H7N9, flu experts in laboratories across the world are picking through the DNA
sequence data of samples isolated from the patients to assess its pandemic
One of the world's top flu experts, Ab Osterhaus, who is based at the Erasmus
Medical Centre in The Netherlands, says the sequences show some genetic
mutations that should put authorities on alert and entail increased surveillance
in animals and humans.
Keeping a close eye
"The virus has to a certain extent already adapted to mammalian species and
to humans, so from that point of view it's worrisome," he said.
"Really we should keep a very close eye on this."
China's National Health and Family Planning Commission confirmed on Sunday
that three people had been infected with the new H7N9 flu, with two deaths of
men in Shanghai aged 87 and 27 who fell sick in late February.
Chinese authorities have in the past two days confirmed another six cases,
including another fatal one.
The World Health Organisation (WHO) says the cases of H7N9 are "of concern"
because they are the first in humans.
"That makes it a unique event, which the World Health Organization is taking
seriously," the Geneva-based United Nations health agency said.
Other strains of bird flu, such as H5N1, have been circulating for many years
and can be transmitted from bird to bird, and bird to human, but not from human
So far, this lack of human-to-human transmission also appears to be a feature
of the H7N9 strain.
Flu viruses are classified based on two types of protein found on their
surface, hemagglutinin and neuraminidase, which are abbreviated to H and N.
Although it is very early, scientists says initial analysis also suggests
H7N9 does not appear to make birds particularly ill - in other words it is what
is known as a low pathogenic avian influenza, of LPAI.
Unfortunately, this doesn't necessarily mean it will be mild in humans, says
Wendy Barclay, a flu virology expert at Britain's Imperial College London.
"We can't be complacent. We have to be cautious," she said, stressing that
other H5 and H7 flu subtypes have been able to mutate from LPAI to the more
dangerous highly pathogenic avian influenza (HPAI) as they circulate in various
hosts, particularly in chickens.
Its mildness in birds could also mean H7N9 is a "silent spreader" - harder to
detect than highly pathogenic flu strains such as H5N1 that can wipe out entire
flocks of wild birds or domestic poultry and are therefore far more visible.
"It's a sort of double-edged sword, because if and when it becomes highly
pathogenic and all the chickens start dying, that's very bad for the poultry
farmers, but it means we can see much more easily where the virus is," Barclay
"At the moment, we can't see where this virus is coming from. We don't know
yet what animal source is feeding this."
Finding that source, and tracking the genetic mutations to see if, how and
when this new strain might gain the ability to spark a human pandemic are now
the priorities for researchers in China and around the world, Barclay and
The WHO praised the Chinese government, saying it was responding to the
situation with various important measures such as enhanced surveillance,
detailed case management and treatment, tracing contacts of all those known to
have been infected so far and training healthcare professionals.
Experts said the fact that H7N9 had been identified and swiftly reported, and
that genetic sequence data was already available for researchers around the
world to analyse, was a sign of how things have changed.
In 2003, China initially tried to cover up an epidemic of Severe Acute
Respiratory Syndrome, which emerged in China and killed about a tenth of the 8
000 people it infected worldwide.
Ian Jones, a professor of virology at Britain's University of Reading, said
the heightened awareness of flu and of the possibility that unusual respiratory
diseases may turn out to be new strains of flu means more cases get referred to
"It's quite possible these cases are being detected because flu is way up
there" on disease priority lists, he said.