At large: Korean pig flu (Image: Jeon Heon-Kyun/EPA/Corbis)

Two weeks ago, a woman died after catching flu from a pig at an agricultural fair in Ohio. Now a new study has found that pigs in Korea are harbouring a similar strain of flu that is more lethal and contagious – 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, 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 acquired two mutations that made it more contagious and more virulent in the animals. The mutated version also grew faster than the original pig virus in cells cultured from the human nose and lung, and in fresh samples of human alveoli. In an intact lung, this alveolar growth could cause lethal pneumonia.


This increase in virulence and transmissibility remained when the team created a virus identical to the original H1N2 but with those two mutations added. That makes this virus apparently more dangerous than the controversial H5N1 bird flu created 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 transmit between them. However, when it was artificially passed from one ferret to another, it mutated and became transmissible. Although it was still lethal in the ferrets’ tracheas, it did not kill when they merely inhaled it.

The work provoked a bitter dispute over whether researchers should create such dangerous viruses or publish the procedures. Similar research on H5N1 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 Tony Fauci, head of the US National Institute for Allergy and Infectious Disease in Bethesda, Maryland, which funded the work.

On the loose?

The original pig virus is probably still circulating in Korea, says co-author 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 effect will disappear over time as that virus no longer circulates.

Of eight leading flu researchers contacted by New Scientist, all – including Michael Osterholm of the University of Minnesota, Minneapolis, who opposed publishing the H5N1 work – insisted that we need research like this to determine what kinds of mutation make pig flu dangerous. And, they emphasised, we need much more surveillance of pigs to see where the viruses are.

“We need to use modern sequencing technology to see what is happening in all the genes,” in pig populations worldwide, says Ab Osterhaus of Erasmus Medical Center in Rotterdam, the Netherlands. “But there is no point just having sequences without research to understand what different mutations do.”

Osterhaus and US flu experts are planning to map mutations known to affect transmission and virulence in flu samples worldwide. Few of the samples will come from pigs, however.

US researchers reported this month 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 and pig handlers. But “considerable barriers exist to conducting surveillance in pigs” they said, partly because this “could economically harm the pork industry”.

Flu sampling in pigs increased in the US and Europe after swine flu caused a pandemic in 2009, says Osterhaus, but some of those projects are ending. “We need much more to know what is happening in pigs.”

Something clearly is happening: 297 people in the US have caught an H3N2 virus from pigs this year, up from 12 last year. One died, and 16 were hospitalised. In Minnesota, three more people caught an H1N2 virus that is slightly different from the Korean virus. All these viruses – including the pandemic – belong to a virulent “triple reassortant” family, which emerged in US pigs in 1998 as a result of a pig flu virus hybridising with a human and bird flu strain. It has been actively evolving ever since.

Journal reference: Proceedings of the National Academy of Science, DOI: 10.1073/pnas.1205576109