SWINE flu is back with a vengeance. Two weeks ago, a woman died after
catching flu from a pig at an agricultural fair in Ohio. Now it seems that pigs
in Korea are harbouring a similar strain of flu that spreads more easily and is
more lethal - at least in animals - than the experimental bird flu that caused
intense controversy last year.
Robert Webster and colleagues at
St Jude Children's Research Hospital in Memphis, Tennessee, put an H1N2 flu
virus, taken from the lungs of a pig slaughtered in South Korea in 2009, into
the noses and windpipes of three ferrets. All the animals died, which is
worrying, as ferrets catch and develop flu in a similar way to humans. What's
more, the virus was transmitted via airborne droplets to three ferrets in
nearby cages, killing two of them.
In passing between the ferrets,
the H1N2 strain acquired two mutations that made it both more contagious and
more virulent. The mutated version also grew faster than the original pig virus
in cells cultured from the human nose and the lung, and in fresh samples of
human alveoli (Proceedings of the National Academy of Sciences, doi.org/jbx).
This increase in virulence and
transmissibility remained when the team added those two mutations to a lab
virus identical to the original H1N2. That makes this virus apparently more
dangerous than the H5N1 bird flu made last year by a group in the Netherlands.
Initially, that virus was only deadly to ferrets when placed in their
windpipes, and it did not transfer between them. However, the virus mutated and
became transmissible when artificially passed between ferrets, though it would
still only kill in the trachea and not when virus droplets were inhaled.
The H5N1 work provoked a bitter
dispute over whether researchers should create such dangerous viruses, or
publish their procedures. Research on that virus remains blocked under a
precautionary moratorium, but no such restrictions apply to H1N2. "This is
important research about something that is already going on in nature,"
says Anthony Fauci, head of the US National Institute for Allergy and
Infectious Diseases in Bethesda, Maryland, which funded the work.
The original pig virus is
probably still circulating in Korea, says co-author of the Korean flu paper
Richard Webby, but no one is known to have caught it. "Either it doesn't
do the same thing in people, or it just hasn't got loose," he says. This
could be because a strain with the same H1 surface protein circulated before
2009, making those exposed to it immune. But this immunity will disappear over
time.
Eight leading flu researchers
were contacted by New Scientist, including Michael Osterholm of the University
of Minnesota, Minneapolis, who objected to the H5N1 work being published. All
insisted that we need research like this to work out what kinds of mutation
make pig flu dangerous.
They also called for more
surveillance of pigs. Flu sampling in pigs increased in the US and Europe after
swine flu caused a pandemic in 2009, says Ab Osterhaus of Erasmus Medical
Center in Rotterdam, the Netherlands. But some of those projects are ending.
"We need to know much more about what is happening in pigs."
Osterhaus and US flu experts plan
to map mutations known to affect transmission and virulence in flu samples
worldwide, though few samples will come from pigs. In a report published this
month, US researchers found that many pigs at agricultural fairs in the US
carry flu, but few show symptoms. They called for more routine sampling and
testing of flu viruses in pigs, but conclude that "considerable barriers
exist", partly because this "could economically harm the pork
industry".
Danger at the agricultural fair
They are supposed to be a fun,
family day out, but the death of an Ohio woman from an H3N2 swine flu virus has
cast a shadow over agricultural fairs, which are thought to attract 150 million
visitors in the US each year. Hers is the only death from this virus so far,
but 297 people caught it this year, mostly at fairs; 16 others needed hospital
treatment, and three passed the virus to others.
Meanwhile, three people in
Minnesota have caught an H1N2 pig virus, a slightly different virus to the
strain found in Korean pigs.
Worryingly, H1N2 and H3N2 may be
better adapted to people than other strains: both carry a gene from the flu
that caused a pandemic in 2009. The gene was incorporated when pigs were
infected with the pandemic virus and seasonal pig flu at the same time.
All these viruses - including the
pandemic strain - belong to a virulent family that emerged in US pigs in 1998
and has been actively evolving ever since.
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