"Just when everybody thought bird flu had disappeared, it has invaded Britain," said Mike Adams, author of "How to Beat the Bird Flu."
"For many Europeans, this means bird flu is now in their own backyard. With two simple mutations, it becomes human transmissible, and that could lead directly to a human pandemic that would quickly spread from nation to nation."
The infected turkeys were found on a farm owned by Bernard Matthews PLC, Europe's largest turkey producer. The virus killed 2,500 of the birds, but all 159,000 turkeys on the farm were immediately marked for slaughter and incineration.
While unusually lethal compared with more common flu strains, H5N1 is not highly contagious. However, it spreads quickly among birds in confined conditions like factory farms and can cross to humans who have close contact with sick birds, particularly poultry workers. Health officials' greatest fear is that the virus could mutate into a much more easily transmissible form.
Such fears are responsible for the wholesale slaughter of infected birds that has become standard policy across the world. In January, thousands of geese were slaughtered by Hungarian officials after the virus was found in the country's southeast.
On the same day that British officials announced the U.K.'s first case of H5N1 in nearly a year, the World Health Organization confirmed the first human death from the virus in Nigeria.
"It bears restating, therefore, that H5N1 is widespread and continuing in the poultry population in Nigeria," said Nigerian Information Minister Frank Nweke.
"This virus is going to be in bird populations for years to come," United Nations Flu Coordinator David Nabarro said. "We have to learn to accept that."