Viral fragments of bird flu have been identified in samples of milk taken from grocery store shelves in the United States, a finding that does not necessarily suggest a threat to human health but indicates the avian flu virus is more widespread among dairy herds than previously thought, according to two public health officials and a public health expert who was briefed on the issue.
The Food and Drug Administration said Tuesday that it had been testing milk samples throughout the dairy production process and confirmed the detection of viral particles “in some of the samples,” but it declined to provide details.
The presence of genetic fragments of the virus in milk is not unexpected. Pasteurization typically works to inactivate pathogens, said Jennifer Nuzzo, director of the Pandemic Center at the Brown University School of Public Health. It generally does not remove genetic material, Nuzzo said, but typically renders pathogens unable to cause harm to people.
The greater concern, however, “is that it’s showing up in a lot more samples, meaning the infection is more widespread in dairy herds than we thought,” said one public health official, who spoke on the condition of anonymity to share information not yet made public.
In a four-page statement, the FDA said some of the samples collected have “indicated the presence” of the bird flu virus based on testing that detects viral particles but does not distinguish whether they are active or dead. The finding of virus “does not mean that the sample contains an intact, infectious pathogen,” the agency’s statement said.
Additional laboratory testing is underway to grow the virus in cells and in fertilized eggs, the latter being the “gold standard” for sensitive detection of active, infectious virus, the FDA said. “Importantly, additional testing is required to determine whether intact pathogen is still present and if it remains infectious, which determines whether there is any risk of illness associated with consuming the product,” the FDA statement said.