The mystery over the origin of Britain's avian flu outbreak deepened today when the Government claimed that the strain of the disease found in Suffolk was "essentially identical" to recent cases in Hungary, but Hungarian officials denied any connection.

Since the outbreak at a Bernard Matthews turkey farm near Holton, in Suffolk, on February 3, public health officials have been closely scrutinising the movement of poultry products to and from the plant and two facilities used by the company in Hungary.

Traces of the deadly H5N1 strain of bird flu were discovered at a goose farm in the eastern Csongrad region of Hungary in the last week of January. Since then, Bernard Matthews has imported and exported meat from a SaGa plant it owns in Sarvar, 160 miles from the outbreak, and an abbatoir at Kecskemet, just miles from the Hungarian exclusion zone.

The coincidence, and similarity between the genetic make-up of the two occurrences of the virus, led the Government's chief scientific adviser, Sir David King, to declare last week that infection from Hungary was "the most likely scenario".

Although the Environment Secretary, David Miliband, insisted yesterday that the investigation continues to study other possibilities, that theory appeared to be strengthened today by Britain's Veterinary Laboratory Agency, which said the Suffolk strain of H5N1 was “essentially identical" to the Hungarian outbreak.

The H5N1 virus that led to the culling of 160,000 turkeys at the Bernard Matthews plant was 99.96 per cent the same as the strain which infected geese in southern Hungary, the VLA found.

“These results indicate that the viruses are essentially identical,” the laboratory's chief avian virologist Ian Brown said in a statement.

"Although other European viruses have shown close relationships to these viruses, these levels of identity are much closer than with other Asian lineage H5 viruses for which data is available, including those isolated from wild birds in Europe in 2005/06."

Britain’s deputy chief vet, Fred Landeg, said the working hypothesis was now that the virus had been transmitted from poultry to poultry rather than through wild birds or other animals. “However, I must reiterate that we are not discounting any line of inquiry and this is an on-going investigation,” he said.

But Hungarian officials have disputed the value of comparing the DNA of the two strains, saying that cases across the world only vary very slightly, and today issued a strong denial of any link between the outbreaks.

Hungary's chief vet, Miklos Suth, reported today that no evidence had been found of how the virus could have spread from meat products in Hungary to Suffolk.

“According to our knowledge today there is no such evidence,” he said in Budapest. “It can almost be ruled out.”

Mr Suth said that the SaGa plant, owned by Bernard Matthews, had no contact with the infected region in the south east of the country, while none of the sources for Gall Foods, the abattoir closer to the exclusion zone, had tested positive for the virus.

Instead, Budapest remains angry that shipments of raw meat continued to be exported from the Bernard Matthews plant to Hungary even after the site was identified as infected, raising the risk that H5N1 was transported back to Central Europe.

Mr Suth pointed out today that 365 tonnes of turkey products were moved from the SaGa site in Sarvar to England between November 2006 and February, while 622 tonnes moved the other way. He said that raw meat exported by Bernard Matthews since the outbreak was confirmed had now been isolated.

The European Commission gave its approval today to the Hungarian inquiry into the outbreak and possible links to the British case. “We are satisfied with the Hungarian investigations and are happy they have acted accordingly,” said a spokesman.

“They told us at a meeting which also included British representatives that they had carried out tests at two Bernard Matthews plants outside of the one where bird flu had been found in Hungary and that there was no suspicion of it there.”

As the likelihood of pinpointing the route by which the H5N1 virus entered the country appeared to recede, turkey slaughtering began once again the Bernard Matthews plant in Suffolk. Yesterday the Meat Hygiene Service (MHS) re-licensed the site's slaughter houses after they had been disinfected.

Today the Department for Environment, Food and Rural Affairs (Defra) said that an MHS inspector would be on hand as birds were brought into the qurantined "protection zone" to be killed.

“They will not come into contact with other birds or meat from the protection zone. There will be no risk to the public. The Food Standards Agency (FSA) advises that avian flu does not pose a food safety risk for UK consumers," Defra said.

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