Virus was ignored for decades

Published on Wednesday 29 April 2009 22:41

SWINE flu showed signs of posing a human pandemic threat more than a decade ago – but the danger was largely ignored, it has been claimed.

A virulent new form of pig flu emerged in the US in 1998, according to a report in New Scientist magazine.

Until then, American pigs had mild attacks of H1N1 flu that affected them every winter.

In 1976, there was an outbreak of swine flu in humans at a military camp in New Jersey with one death. The virus was not able to spread and soon "fizzled out".

But in 1998 the H1N1 strain combined with both human and bird viruses to produce "triple reassortants" that surfaced in Minnesota, Iowa and Texas.

This was a much more aggressive form of flu that should have set alarm bells ringing, according to New Scientist.

The bird element – two genes for the RNA polymerase enzyme – allowed the viruses to replicate rapidly and become more virulent. By 1999, they had become the dominant flu strain in North American pigs and were actively evolving, the report said.

Many different versions evolved, making the creation of a strain that could infect humans more likely. And by switching surface proteins, the viruses adapted to evade the pig immune system.

Today there are so many kinds of swine flu that outbreaks at pig farms are no longer seasonal, New Scientist said.

One in five US pig producers was said to make its own vaccines because the vaccine industry could not keep up with the changes.

One US expert, Richard Webby from St Jude's Children's Research Hospital in Memphis, Tennessee, warned back in 2004 that pigs in the US were "an increasingly important reservoir of viruses with human pandemic potential", the report added.