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H1N1 Was In Pigs For Years: Study

“This lineage has been circulating under the radar for the better part of a decade.”

– MICHAEL WOROBEY

Ever since the H1N1 flu virus emerged earlier this year, pork producers have objected to its commonly used name: swine flu.

Producers argue the virus is about people, not pigs, and the term is unfair to themselves and their industry.

However, new research in the United States suggests H1N1 was circulating in pigs for years before it mutated and jumped to humans.

A recent study looked at the genetic sequences from H1N1, compared them to older samples and tracked the evolution of the 2009 pandemic.

It concluded the virus was circulating in pigs for about 10 years before it moved into the human population.

“We get the same pattern from each of these genomic segments and that suggests that this lineage has been circulating under the radar for the better part of a decade,” said Michael Worobey, a University of Arizona scientist and co-author of the study.

“The most plausible interpretation is that this virus has been circulating and very recently made the jump.”

The study appeared in a recent issue of Nature magazine. Worobey presented it at a meeting of flu experts sponsored by the U. S. Institute of Medicine last week in Washington, D. C.

First identified in Mexico in March 2009, H1N1 has since spread throughout the human population worldwide. It has been also found in a few swine herds, most lately in Manitoba. But that’s the human strain gone back into pigs, not the original strain itself.

In an interview from Washington, Worobey said the fact that this disease originated in animals and mutated to create a human pandemic is not new. This happened several times in the 20th century, most notably during the Spanish flu pandemic of 1918-19.

But it shows the need for increased surveillance for flu viruses in swine herds, he said.

The U. S. Department of Agriculture last week announced a voluntary surveillance plan for swine influenza, including the H1N1 virus.

Dr. Wayne Lees, Manitoba’s provincial veterinarian, welcomed the USDA’s move. But he said Manitoba and other provinces have long conducted ongoing surveillance for influenza and other livestock diseases using samples submitted regularly to the provincial veterinary laboratory.

That’s how H1N1 was detected in several Manitoba swine herds this summer, he said.

Lees also expressed skepticism that H1N1 had been circulating in pigs for years before it jumped to humans.

Any new and unusual swine disease would have shown up in routine diagnostic submissions long ago if that were the case, he said.

A flu strain is often a combination of gene sequences. The H1N1 virus is a hybrid strain with genetic similarities to swine, human and avian flu rolled into one.

The fact that some of its pieces may have been around for a long time is not particularly relevant, said Lees.

“That really doesn’t translate into anything.” [email protected]

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