Flu viruses rode on pig imports into southern China - study

HONG KONG Wed May 25, 2011 12:59pm EDT

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HONG KONG May 26 (Reuters) - China may have unwittingly introduced swine flu viruses when it imported pigs from Europe and North America for breeding over the past few decades, researchers said.

Three virus families are endemic in pigs in southern China and one of them - the Eurasian avian-like H1N1 flu virus from Europe - is viewed as most threatening because humans have no antibodies against it, said the researchers, who published their findings in Nature magazine on Thursday.

The researchers in Hong Kong, Singapore and China reached their findings after monitoring swine flu viruses in pigs in Hong Kong over a 12-year period.

"We found that since 2001, the Eurasian (flu) viruses and North American viruses had entered pig populations in southern China and replaced the earlier viruses," said Vijaykrishna Dhanasekaran, assistant professor at the Duke-NUS Graduate Medical School's Program of Emerging Infectious Diseases in Singapore.     "The import of breeding pigs has increased in southern China over the 20 years, this was done to improve the breeds," he said by telephone from Singapore.

From 1998 to 2010, Dhanasekaran and colleagues collected more than than 650 flu virus samples from pigs that ended up in a Hong Kong abattoir and found they all belonged to three lineages.

The most dominant was the Eurasian avian-like H1N1 virus. First detected in pigs in Belgium in 1979, it quickly became the most common flu virus in pigs in Europe.

The other 2 lineages are the North American H1N2 swine flu virus which has been circulating in pigs in North America since the 1990s and the H1N1 swine flu virus which has been circulating worldwide, including in China, for more than 80 years.

VIRUSES RODE ON BREEDING PIGS

"The introduction could have most likely been the breeding pigs ... Now we have a better understanding of how viruses travel globally," said Dhanasekaran.

The Eurasian avian-like virus was potentially most problematic because people do not have immunity, or antibodies, to fight it, he said.

"We have this Eurasian avian-like H1N1 virus which we don't have any antibodies (against) ... and it is likely that this virus can spread among humans easily," he said.

He urged other regions to conduct similar disease surveillance in animals.

"The diversity in other areas can be different and what they should do is conduct surveillance and target viruses that we don't have antibodies towards and these would most likely be candidates for pandemic preparedness," Dhanasekaran said.

What experts fear are animal viruses new to people making a jump to humans and sparking a pandemic. This was how the H5N1 bird flu virus and SARS spread around much of the world in 2003. In 2009, a novel H1N1 swine flu virus caused a pandemic.

Eighty to 95 percent of pigs slaughtered in Hong Kong originate in southern China, which has the largest swine population in the world. (Editing by Robert Birsel) (Created by Ee-lyn Tan)

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