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An American scientist says he was misquoted as saying the swine flu virus originated in "either New Zealand or China".

The director of Louisiana State University's division of biotechnology and molecular medicine, Gus Kousoulas, had been quoted as saying: "We think it [swine flu] began in New Zealand or China."

But he subsequently told the New Zealand Science Media Centre: "The statement was based on early phylogenetic analysis of available sequences. It was misquoted.

"There is no basis currently to support a New Zealand origin. While we still do not know the true origin, a US or Mexico origin is more likely," he added.

New Zealand's Director of Public Health, Mark Jacobs, said last night any link would be very surprising, "given that our small number of confirmed cases are from travellers returning from overseas".

"New Zealand has an excellent influenza surveillance system and this strain has not been detected here previously."

The World Health Organisation says 53 countries have reported 15,510 cases of swine flu - influenza A (H1N1). Most cases have been in the US and Mexico.

Ninety-nine people have died.

New Zealand has had 30 suspected cases, and 23 people were placed in isolation or quarantine and treated with Tamiflu.

"The cumulative total of known past infections remains at nine, with all cases fully recovered," a Health Ministry statement said.

The Louisiana biotechnology division specialises in research on zoonotic diseases - those animals can transmit to humans - and Dr Kousoulas said his researchers had been focusing on the H1N1 virus.

"If the avian flu and human flu infect a pig, the pig becomes a mixing vessel," he said.

"The viruses mix in the pig, and a new virus comes out. Because it changes so fast, it is highly possible that a new virus evolves that is highly virulent in humans."

Companies that produce vaccines were now faced with a dilemma over whether they should produce vaccines for seasonal flu, swine flu or both, Dr Kousoulas said.

"If we produce both vaccines, then we will have to produce much less of each, which means not everybody could be immunised."

Another fear was that swine flu would mutate so much that the new vaccine would be useless by the time seasonal flu returned to North America in the New Zealand spring.

"Now we're all holding our breath to see what happens in the Southern Hemisphere."

The research centre been given US$10 million ($15.4 million) from the US National Institutes of Health to create a centre for experimental infectious disease research.

"We're interested in every virus or bacterium that could infect animals or a human."

New Zealand virologist Dr Richard Webby, who is at St Jude Children's Research Hospital in Memphis and is director of the World Health Organisation's collaborating centre for studies on the ecology of influenza viruses in animals and birds, has found the A (H1N1) virus to be specifically a swine virus.

Other researchers have shown that some of the eight segments that make up the swine flu virus are related to influenza viruses found in swine in North America and Eurasia, and that segments from the North American lineage are related to a swine virus isolated in 1998 that stemmed from avian, swine and human viruses.