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.