A report into the outbreak of bird flu at a quarantine centre in Essex has suggested that the deadly H5N1 strain of the virus - blamed for more than 60 human deaths in Asia - may not be as easily transmitted between species of birds as previously feared.

The report, by the National Emergency Epidemiology Group, published today by the Department for Environment, Food and Rural Affairs, found that a South American parrot originally thought to have brought in the virus was in fact clear of the disease and the most likely source was a consignment of finches from Taiwan.

More than 50 of the mesia finches, out of a consignment of 101, died before the outbreak was discovered. The H5N1 virus was isolated from three of those birds, although others may have been infected.

The rest of the consignment were humanely killed, but none displayed any sign of the virus. More importantly, none of the other species imported with the mesias - 20 black-throat laughing thrushes and 65 mynah birds - showed sign of the disease either. Four 'sentinel fowl' also kept in the quarantine centre did not contract the virus either.

All seven species of birds in a consignment from Surinam which arrived at the centre 11 days before the Taiwan consignment were also free of the virus.

Debby Reynolds, the Chief Veterinary Officer, said: "This report contains significant epidemiological findings and helps to further our understanding of highly pathogenic avian influenza.

"In particular the apparent lack of transmission of H5N1 between species in the facility will be of interest to the international community. The available evidence points to the mesias, which were documented as imported from Taiwan, as the most likely source of the virus."

The report does have diplomatic implications. Taiwan has denied that any of the birds that it exports suffer from bird flu. But the epidemiologists said that the "molecular genetic characterisation" of the H5N1 isolated did not match those found in Europe recently, but was "closely associated" with an isolate from Chinese ducks tested earlier this year.

The confusion over the dead parrot appears to have arisen because the first batch of tissue sample sent for testing at the reference laboratory in Weybridge contained samples both from a mesia and a blue-headed pionus parrot. The mistake was not noticed for about a week, by which time the parrot had already been blamed.

Ben Bradshaw, the Environment Minister, told the BBC that there was no evidence to support an Opposition claim that any of the birds had escaped or been released. He said the most significant finding of the report was that the lack of transmission between species.

"That has pretty significant implications for bird flu internationally, particularly among wild birds," he said.

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