Tests of birds at the quarantine center where Britain's first case was detected showed that the virulent H5N1 strain was present only within a group of Mesias imported from Taiwan, a report from the Department for Environment, Food and Rural Affairs said.

The department said the H5N1 strain had been isolated in samples taken from some of the 53 Mesias that died in quarantine before Oct. 21, when bird flu was first confirmed. All the birds in the center were subsequently destroyed.

Significant Epidemiological Findings

The department said five pools of viscera from 30 of the 53 birds were analyzed, and the avian flu virus was found in three of the five pools.

There was no trace of avian flu among the healthy Mesias that were destroyed, the department said.

"This report contains significant epidemiological findings and helps to further our understanding of Highly Pathogenic Avian Influenza," Chief Veterinary Officer Debby Reynolds said.

"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."

Origin of the Infection

The H5N1 virus isolated in Britain closely matched the strain of the disease previously identified in ducks in China, the report said.

"Within the species documented as coming from Taiwan only the Mesias were infected with H5N1 and 53 out of 101 birds had died," said Margaret Beckett, the Cabinet minister who heads the department.

"This is consistent with DEFRA's working hypothesis of Oct. 23 that the likeliest origin of the infection was the birds from Taiwan," Beckett said in a written statement to Parliament.