Saturday, September 15, 2012
USA - Swine flu evolves under the radar
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.