By Kate Kelland, Health and Science Correspondent
LONDON (Reuters) - A big wave of H7N9 bird flu cases and deaths in
China since the start of 2014 is a reminder that emerging flu strains
need constant surveillance if the world is not to be caught off guard by
a deadly pandemic.
At least 24 H7N9 flu infections and three deaths have been confirmed
in the past week by the World Health Organisation (WHO), a dramatic
increase on the two cases and one death reported for the four-month
summer period of June to September.
"There's now a clear second wave of this virus," said Jake Dunning, a
researcher at Imperial College London who has been monitoring the
outbreak.
While the winter flu season means an increase in infections is not
unexpected, it also raises the risk of the virus mutating and perhaps
getting a chance to acquire genetic changes that may allow it to spread
easily from one person to another.
The H7N9 bird flu virus first emerged in March last year and has so
far infected at least 170 people in China, Taiwan and Hong Kong, killing
around 50 of them.
Many but not all of the people infected have had previous contact
with poultry or other birds, so for now, the fact that this virus has
apparently not adapted to easy human-to-human transmission is one of the
main features keeping a pandemic emergency response on hold.
Yet the strain already has several worrisome features, including a limited capability to spread from one person to another.
CLUSTERS
Several clusters of cases in people who had close contact with an
initially infected person have been reported in China. A scientific
analysis of probable H7N9 transmission from person to person, published
last August, gave the best proof yet that it can sporadically jump
between people.
A separate team of researchers in the United States said in December
that while it is not impossible that H7N9 could become easily
transmissible from person to person, it would need to undergo multiple
mutations to do that.
Another alarm was sounded, also last month, when scientists said
they had found that a mutation in the virus can render it resistant to a
key first-line treatment drug without limiting its ability to spread in
mammals.
WHO chief spokesman Gregory Hartl told Reuters the United Nations
health agency had noted the rapid increase in infections in the past few
weeks and is keeping a watchful eye.
"So far we haven't seen anything that cause us to change our risk assessment," he said from WHO's Geneva headquarters
The WHO's current stance, based on its December 20 assessment, is
that five small family clusters have been reported but "evidence does
not currently support sustained human-to-human transmission of this
virus."
"The current likelihood of community-level spread... is considered to be low," it says.
Flu viruses, however, often put on their biggest show of strength in the cold winter months of January and February.
And with more of the virus circulating in wild birds, poultry and in
the larger numbers of people infected in China and elsewhere, the new
strain now has more opportunity to adapt and mix with other strains that
may give it pandemic potential.
MIX AND MINGLE
Peter Openshaw, director of the Centre for Respiratory Infection at
Imperial College London, said the rising toll of infections and deaths
is "a signal for concern" because "historically what has happened in
major outbreaks is there are occasional, sporadic cases and then it
starts to build".
"But whether it means that there is any change in the virus'
behavior is another important question. If it were changing the way it
is behaving, that would be more alarming," he told Reuters.
Early gene analysis work on the emerging H7N9 virus in April last
year found it had already been circulating widely but went undetected.
During that activity, it had also acquired significant genetic
diversity, making it more of a threat.
Scientists warned then that its genetic diversity showed the H7N9
virus has an ability to mutate repeatedly and was likely to continue
doing so.
Dunning noted also that H7N9 is now more likely to meet and
potentially mix with other seasonal flu virus strains such as H1N1 and
H3N2, which are circulating widely among people in China at the moment.
"When you get hybrid viruses forming, that tends to occur in other
species, but there is always the potential for it to happen in humans,"
he said. "So that is a theoretical concern."
Hartl agreed that the opportunity for the virus to take on more
features and capabilities is now greater, but stressed that such changes
may not necessarily present fresh dangers.
"Mutations happen all the time," he said. "And while yes, the more
virus there is, the more mutations could happen, it's also true that
almost all of these mutations are benign."
(Reporting by Kate Kelland; Editing by Tom Heneghan)
end quote from:
What is presently killing people under 40 mostly in the U.S. is the H1N1 and not the H7N9 strain.
No comments:
Post a Comment